diff --git a/iosApp/iosApp/Sources/ui/home/HomeViewModel.swift b/iosApp/iosApp/Sources/ui/home/HomeViewModel.swift
index 4022b3a..54cdf2b 100644
--- a/iosApp/iosApp/Sources/ui/home/HomeViewModel.swift
+++ b/iosApp/iosApp/Sources/ui/home/HomeViewModel.swift
@@ -25,34 +25,44 @@ class HomeViewModel: ObservableObject {
         viewState = .initialLoading
         
         do {
-            async let userDefered = userUseCase.findForIos()
-            async let pointDefered = pointUseCase.findForIos()
-            async let historyDefered = historyUseCase.findAllForIos()
+            async let userDefered = userUseCase.find()
+            async let pointDefered = pointUseCase.find()
+            async let historyDefered = historyUseCase.findAll()
 
             let (userResult, pointResult, historiesResult) = try await (userDefered, pointDefered, historyDefered)
-            viewState = .loaded(
-                user: userResult,
-                point: Int(pointResult.balance)
-            )
-            historyState = .loaded(histories: historiesResult)
+            
+            var user: User?
+            
+            switch asEnumResult(result: userResult) {
+            case .success(let userResult):
+                user = userResult
+            case .error(let error):
+                viewState = .error(message: error.message)
+            }
+            
+            switch asEnumResult(result: pointResult) {
+            case .success(let pointResult):
+                viewState = .loaded(
+                    user: user!,
+                    point: Int(pointResult.balance)
+                )
+            case .error(let error):
+                viewState = .error(message: error.message)
+            }
+            
+            switch asEnumResult(result: historiesResult) {
+            case .success(let data):
+                // Kotlin/Native の List<T> は Swift 側では [T] ではない場合があります。
+                // そのため、ここは既存動作を保ちつつ安全にキャストを試みます。
+                if let historiesResult = data as? [PointHistory] {
+                    historyState = .loaded(histories: historiesResult)
+                }
+            case .error(let error):
+                viewState = .error(message: error.message)
+            }
         } catch is CancellationError {
             // no operation(not change UI)
             return
-        } catch let e as AppError {
-            switch (e) {
-            case is AppError.NetworkError:
-                viewState = .error(message: e.message)
-                break
-            case is AppError.ProgramError:
-                viewState = .error(message: e.message)
-                break
-            case is AppError.UnknownError:
-                viewState = .error(message: e.message)
-                break
-            default:
-                viewState = .error(message: e.message)
-                break
-            }
         } catch {
             viewState = .error(message: "Unknown Error")
         }
diff --git a/iosApp/iosApp/Sources/ui/pointget/PointGetViewModel.swift b/iosApp/iosApp/Sources/ui/pointget/PointGetViewModel.swift
index e87c563..9a50d2e 100644
--- a/iosApp/iosApp/Sources/ui/pointget/PointGetViewModel.swift
+++ b/iosApp/iosApp/Sources/ui/pointget/PointGetViewModel.swift
@@ -17,13 +17,18 @@ class PointGetViewModel: ObservableObject {
     @MainActor
     func load() async {
         do {
-            let point = try await pointUseCase.findForIos()
-            viewState = .success(
-                currentPoint: point,
-                inputPoint: 0,
-                errorMessage: nil,
-                isEnableConfirm: false
-            )
+            let result = try await pointUseCase.find()
+            switch asEnumResult(result: result) {
+            case .success(let point):
+                viewState = .success(
+                    currentPoint: point,
+                    inputPoint: 0,
+                    errorMessage: nil,
+                    isEnableConfirm: false
+                )
+            case .error(error: let error):
+                viewState = .error(message: error.message)
+            }
         } catch {
             viewState = .error(message: "ポイント残高の取得に失敗しました。")
         }
@@ -80,4 +85,3 @@ enum PointAcquireEventState: Equatable {
     case success
     case error(message: String)
 }
-
diff --git a/iosApp/iosApp/Sources/ui/slpash/SplashViewModel.swift b/iosApp/iosApp/Sources/ui/slpash/SplashViewModel.swift
index 76b83ed..35d4c36 100644
--- a/iosApp/iosApp/Sources/ui/slpash/SplashViewModel.swift
+++ b/iosApp/iosApp/Sources/ui/slpash/SplashViewModel.swift
@@ -15,11 +15,16 @@ class SplashViewModel: ObservableObject {
     func load() async {
         viewState = .loading
         do {
-            let user = try await userUseCase.findForIos()
-            if user.isInitialized(), let userId = user.userId {
-                self.viewState = .loaded(userId: userId)
-            } else {
-                self.viewState = .firstTime
+            let result = try await userUseCase.find()
+            switch asEnumResult(result: result) {
+            case .success(data: let user):
+                if user.isInitialized(), let userId = user.userId {
+                    self.viewState = .loaded(userId: userId)
+                } else {
+                    self.viewState = .firstTime
+                }
+            case .error(error: let error):
+                self.viewState = .error(message: error.message)
             }
         } catch is CancellationError {
             // no operation(not change UI)
diff --git a/iosApp/iosApp/Sources/ui/start/StartViewModel.swift b/iosApp/iosApp/Sources/ui/start/StartViewModel.swift
index 3673715..1c08bd3 100644
--- a/iosApp/iosApp/Sources/ui/start/StartViewModel.swift
+++ b/iosApp/iosApp/Sources/ui/start/StartViewModel.swift
@@ -19,8 +19,14 @@ class StartViewModel: ObservableObject {
         viewState = .loading
         
         do {
-            try await userUseCase.registerUserForIos(nickname: nickname, email: email)
-            viewState = .success
+            let result = try await userUseCase.registerUser(nickname: nickname, email: email)
+            switch asEnumComplete(complete: result) {
+            case .complete:
+                viewState = .success
+            case .error(let error):
+                viewState = .idle
+                errorAlertItem = StartErrorAlertItem(message: error.message)
+            }
         } catch is CancellationError {
             // no operation(not change UI)
             return
diff --git a/iosApp/iosApp/Sources/util/Extension.swift b/iosApp/iosApp/Sources/util/Extension.swift
new file mode 100644
index 0000000..4487979
--- /dev/null
+++ b/iosApp/iosApp/Sources/util/Extension.swift
@@ -0,0 +1,56 @@
+//
+//  Extension.swift
+//  iosApp
+//
+import Foundation
+import shared
+
+// Sealed Classが使いづらいのでAppResultをEnumにする
+enum AppResultEx<T> {
+    case success(data: T)
+    case error(error: AppError)
+}
+
+func asEnumResult<T>(result: AppResult<T>) -> AppResultEx<T> {
+    if let success = result as? AppResultSuccess<T> {
+        // Kotlin/Native ではジェネリクス T が Swift 側で T? として表現されることがあるため明示的にアンラップ
+        if let data = success.data {
+            return .success(data: data)
+        }
+        fatalError(#function + ": Success の data が nil です（想定外）")
+    }
+    if let failure = result as? AppResultError {
+        return .error(error: failure.error)
+    }
+    fatalError(#function + ": 想定外のAppResultです")
+}
+
+// Sealed Classが使いづらいのでAppCompleteをEnumにする
+enum AppCompleteEx {
+    case complete
+    case error(error: AppError)
+}
+
+func asEnumComplete(complete: AppComplete) -> AppCompleteEx {
+    if complete is AppComplete.Complete {
+        return .complete
+    }
+    if let failure = complete as? AppComplete.Error {
+        return .error(error: failure.error)
+    }
+    fatalError(#function + ": 想定外のAppCompleteです")
+}
+
+// KMPのBooleanをSwiftのBoolに変換する拡張関数（オプショナル型）
+extension Optional where Wrapped == shared.KotlinBoolean {
+    var asBool: Bool {
+        return self?.boolValue ?? false
+    }
+}
+
+// KMPのBooleanをSwiftのBoolに変換する拡張関数
+extension shared.KotlinBoolean {
+    var asBool: Bool {
+        return self.boolValue
+    }
+}
diff --git a/shared/src/commonMain/kotlin/jp/hotdrop/considercline/model/AppError.kt b/shared/src/commonMain/kotlin/jp/hotdrop/considercline/model/AppError.kt
index a1d031c..9f1c0ad 100644
--- a/shared/src/commonMain/kotlin/jp/hotdrop/considercline/model/AppError.kt
+++ b/shared/src/commonMain/kotlin/jp/hotdrop/considercline/model/AppError.kt
@@ -1,7 +1,5 @@
 package jp.hotdrop.considercline.model
 
-import kotlin.coroutines.cancellation.CancellationException
-
 sealed class AppError {
     data class NetworkError(val error: Throwable): AppError()
     data class UnknownError(val error: Throwable): AppError()
@@ -15,17 +13,4 @@ sealed class AppError {
         }
 }
 
-fun mapToDomain(appError: AppError): Throwable =
-    when (appError) {
-        is AppError.NetworkError -> appError.error
-        is AppError.UnknownError -> appError.error
-        is AppError.ProgramError -> ProgramException(appError.message)
-    }
-
-fun mapToThrowable(t: Throwable): AppError =
-    when (t) {
-        is CancellationException -> throw t
-        else -> AppError.UnknownError(t)
-    }
-
 data class ProgramException(val errorMessage: String): Exception(errorMessage)
\ No newline at end of file
diff --git a/shared/src/commonMain/kotlin/jp/hotdrop/considercline/usecase/HistoryUseCase.kt b/shared/src/commonMain/kotlin/jp/hotdrop/considercline/usecase/HistoryUseCase.kt
index d789340..07d96e8 100644
--- a/shared/src/commonMain/kotlin/jp/hotdrop/considercline/usecase/HistoryUseCase.kt
+++ b/shared/src/commonMain/kotlin/jp/hotdrop/considercline/usecase/HistoryUseCase.kt
@@ -1,25 +1,22 @@
 package jp.hotdrop.considercline.usecase
 
+import jp.hotdrop.considercline.model.AppError
 import jp.hotdrop.considercline.model.AppResult
 import jp.hotdrop.considercline.model.PointHistory
-import jp.hotdrop.considercline.model.mapToDomain
 import jp.hotdrop.considercline.repository.HistoryRepository
+import kotlin.coroutines.cancellation.CancellationException
 
 class HistoryUseCase(
     private val repository: HistoryRepository
 ) {
     suspend fun findAll(): AppResult<List<PointHistory>> {
-        return fetchHistories()
-    }
-
-    suspend fun findAllForIos(): List<PointHistory> {
-        return when(val result = fetchHistories()) {
-            is AppResult.Success -> result.data
-            is AppResult.Error -> throw mapToDomain(result.error)
+        return runCatching {
+            repository.findAll()
+        }.getOrElse { throwable ->
+            if (throwable is CancellationException) {
+                throw throwable
+            }
+            AppResult.Error(AppError.UnknownError(throwable))
         }
     }
-
-    private suspend fun fetchHistories(): AppResult<List<PointHistory>> {
-        return repository.findAll()
-    }
 }
\ No newline at end of file
diff --git a/shared/src/commonMain/kotlin/jp/hotdrop/considercline/usecase/PointUseCase.kt b/shared/src/commonMain/kotlin/jp/hotdrop/considercline/usecase/PointUseCase.kt
index 4efca41..c38febe 100644
--- a/shared/src/commonMain/kotlin/jp/hotdrop/considercline/usecase/PointUseCase.kt
+++ b/shared/src/commonMain/kotlin/jp/hotdrop/considercline/usecase/PointUseCase.kt
@@ -1,63 +1,52 @@
 package jp.hotdrop.considercline.usecase
 
 import jp.hotdrop.considercline.model.AppComplete
+import jp.hotdrop.considercline.model.AppError
 import jp.hotdrop.considercline.model.AppResult
 import jp.hotdrop.considercline.model.Point
 import jp.hotdrop.considercline.model.flatMap
-import jp.hotdrop.considercline.model.mapToDomain
 import jp.hotdrop.considercline.repository.HistoryRepository
 import jp.hotdrop.considercline.repository.PointRepository
+import kotlin.coroutines.cancellation.CancellationException
 
 class PointUseCase(
     private val pointRepository: PointRepository,
     private val historyRepository: HistoryRepository
 ) {
     suspend fun find(): AppResult<Point> {
-        return fetchPoint()
-    }
-
-    suspend fun findForIos(): Point {
-        return when(val result = fetchPoint()) {
-            is AppResult.Success -> result.data
-            is AppResult.Error -> throw mapToDomain(result.error)
+        return runCatching {
+            pointRepository.find()
+        }.getOrElse { throwable ->
+            if (throwable is CancellationException) {
+                throw throwable
+            }
+            AppResult.Error(AppError.UnknownError(throwable))
         }
     }
 
-    private suspend fun fetchPoint(): AppResult<Point> {
-        return pointRepository.find()
-    }
-
     suspend fun acquire(inputPoint: Int): AppComplete {
-        return acquireToRepo(inputPoint)
-    }
-
-    suspend fun acquireForIos(inputPoint: Int) {
-        return when(val result = acquireToRepo(inputPoint)) {
-            is AppComplete.Complete -> Unit
-            is AppComplete.Error -> throw mapToDomain(result.error)
-        }
-    }
-
-    private suspend fun acquireToRepo(inputPoint: Int): AppComplete {
-        return pointRepository.acquire(inputPoint).flatMap {
-            historyRepository.saveAcquire(inputPoint)
+        return runCatching {
+            pointRepository.acquire(inputPoint).flatMap {
+                historyRepository.saveAcquire(inputPoint)
+            }
+        }.getOrElse { throwable ->
+            if (throwable is CancellationException) {
+                throw throwable
+            }
+            AppComplete.Error(AppError.UnknownError(throwable))
         }
     }
 
     suspend fun use(inputPoint: Int): AppComplete {
-        return useToRepo(inputPoint)
-    }
-
-    suspend fun useForIos(inputPoint: Int) {
-        return when(val result = useToRepo(inputPoint)) {
-            is AppComplete.Complete -> Unit
-            is AppComplete.Error -> throw mapToDomain(result.error)
-        }
-    }
-
-    private suspend fun useToRepo(inputPoint: Int): AppComplete {
-        return pointRepository.use(inputPoint).flatMap {
-            historyRepository.saveUse(inputPoint)
+        return runCatching {
+            pointRepository.use(inputPoint).flatMap {
+                historyRepository.saveUse(inputPoint)
+            }
+        }.getOrElse { throwable ->
+            if (throwable is CancellationException) {
+                throw throwable
+            }
+            AppComplete.Error(AppError.UnknownError(throwable))
         }
     }
 }
\ No newline at end of file
diff --git a/shared/src/commonMain/kotlin/jp/hotdrop/considercline/usecase/UserUseCase.kt b/shared/src/commonMain/kotlin/jp/hotdrop/considercline/usecase/UserUseCase.kt
index f0b0772..78876f7 100644
--- a/shared/src/commonMain/kotlin/jp/hotdrop/considercline/usecase/UserUseCase.kt
+++ b/shared/src/commonMain/kotlin/jp/hotdrop/considercline/usecase/UserUseCase.kt
@@ -1,41 +1,34 @@
 package jp.hotdrop.considercline.usecase
 
 import jp.hotdrop.considercline.model.AppComplete
+import jp.hotdrop.considercline.model.AppError
 import jp.hotdrop.considercline.model.AppResult
 import jp.hotdrop.considercline.model.User
-import jp.hotdrop.considercline.model.mapToDomain
 import jp.hotdrop.considercline.repository.UserRepository
+import kotlin.coroutines.cancellation.CancellationException
 
 class UserUseCase(
     private val userRepository: UserRepository
 ) {
     suspend fun find(): AppResult<User> {
-        return fetchUser()
-    }
-
-    suspend fun findForIos(): User {
-        return when (val result = fetchUser()) {
-            is AppResult.Success -> result.data
-            is AppResult.Error -> throw mapToDomain(result.error)
+        return runCatching {
+            userRepository.find()
+        }.getOrElse { throwable ->
+            if (throwable is CancellationException) {
+                throw throwable
+            }
+            AppResult.Error(AppError.UnknownError(throwable))
         }
     }
 
-    private suspend fun fetchUser(): AppResult<User> {
-        return userRepository.find()
-    }
-
     suspend fun registerUser(nickname: String?, email: String?): AppComplete {
-        return saveRegisterUser(nickname, email)
-    }
-
-    suspend fun registerUserForIos(nickname: String?, email: String?) {
-        return when (val result = saveRegisterUser(nickname, email)) {
-            is AppComplete.Complete -> Unit
-            is AppComplete.Error -> throw mapToDomain(result.error)
+        return runCatching {
+            userRepository.registerUser(nickname, email)
+        }.getOrElse { throwable ->
+            if (throwable is CancellationException) {
+                throw throwable
+            }
+            AppComplete.Error(AppError.UnknownError(throwable))
         }
     }
-
-    private suspend fun saveRegisterUser(nickname: String?, email: String?): AppComplete {
-        return userRepository.registerUser(nickname, email)
-    }
 }
\ No newline at end of file