diff --git a/src/errors/ErrorHandler.ts b/src/errors/ErrorHandler.ts
index fff624d..bf2ef8d 100644
--- a/src/errors/ErrorHandler.ts
+++ b/src/errors/ErrorHandler.ts
@@ -106,7 +106,7 @@ export class ErrorHandler implements IDisposable {
         // i18n service might not be available yet during initialization
         try {
             this.i18n = getI18n();
-        } catch (_error) {
+        } catch {
             // i18n service will be available later
         }
 
@@ -130,22 +130,21 @@ export class ErrorHandler implements IDisposable {
         // Unhandled promise rejections
         this.unhandledRejectionHandler = (event: PromiseRejectionEvent) => {
             // Filter out errors that are not from our plugin
-            const error = event.reason;
-            const errorString = error?.toString?.() || String(error);
+            const reasonSummary = this.describeReason(event.reason);
 
             // Ignore errors from other plugins/sources
-            if (errorString.includes('inputEl') ||
-                errorString.includes('Cannot read properties of undefined') ||
-                !errorString.includes('voice-input')) {
+            if (reasonSummary.includes('inputEl') ||
+                reasonSummary.includes('Cannot read properties of undefined') ||
+                !reasonSummary.includes('voice-input')) {
                 // Log in development mode only
                 if (this.options.isDevelopment) {
-                    this.logger.debug('[VoiceInput] Ignored external error', error);
+                    this.logger.debug('[VoiceInput] Ignored external error', { reason: reasonSummary });
                 }
                 return;
             }
 
             this.handleError(
-                new Error(`Unhandled Promise Rejection: ${event.reason}`),
+                new Error(`Unhandled Promise Rejection: ${reasonSummary}`),
                 {
                     component: 'Global',
                     operation: 'UnhandledRejection',
@@ -159,8 +158,9 @@ export class ErrorHandler implements IDisposable {
 
         // Global error events
         this.errorHandler = (event: ErrorEvent) => {
+            const eventError = event.error instanceof Error ? event.error : new Error(event.message);
             this.handleError(
-                event.error || new Error(event.message),
+                eventError,
                 {
                     component: 'Global',
                     operation: 'UncaughtError',
@@ -247,7 +247,7 @@ export class ErrorHandler implements IDisposable {
         let contextSummary: string;
         try {
             contextSummary = JSON.stringify(context);
-        } catch (_error) {
+        } catch {
             contextSummary = '[Unserializable context]';
         }
         throw lastError || new Error(`Retry operation failed after ${this.options.maxRetries} attempts in context: ${contextSummary}`);
@@ -319,6 +319,20 @@ export class ErrorHandler implements IDisposable {
         }
     }
 
+    private describeReason(reason: unknown): string {
+        if (typeof reason === 'string') {
+            return reason;
+        }
+        if (reason instanceof Error) {
+            return reason.message || reason.name;
+        }
+        try {
+            return JSON.stringify(reason);
+        } catch {
+            return String(reason);
+        }
+    }
+
     /**
      * ユーザーに通知
      */
@@ -343,7 +357,7 @@ export class ErrorHandler implements IDisposable {
         if (!this.i18n) {
             try {
                 this.i18n = getI18n();
-            } catch (_error) {
+            } catch {
                 // Fallback to English messages
                 switch (severity) {
                     case ErrorSeverity.FATAL:
diff --git a/src/errors/TranscriptionError.ts b/src/errors/TranscriptionError.ts
index 61ba645..283260a 100644
--- a/src/errors/TranscriptionError.ts
+++ b/src/errors/TranscriptionError.ts
@@ -37,7 +37,7 @@ export class TranscriptionError extends Error {
 
         try {
             i18n = getI18n();
-        } catch (_error) {
+        } catch {
             // Fallback to original message if i18n is not available
             return this.message;
         }
diff --git a/src/main.ts b/src/main.ts
index 598b425..462da75 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -1,2 +1,2 @@
 // Main entry point for Voice Memo Plugin
-export { default } from './plugin';
\ No newline at end of file
+export { default } from './plugin';
diff --git a/src/managers/ViewManager.ts b/src/managers/ViewManager.ts
index cac0282..f28ee5b 100644
--- a/src/managers/ViewManager.ts
+++ b/src/managers/ViewManager.ts
@@ -21,7 +21,7 @@ export class ViewManager extends Disposable {
         // ServiceLocatorからLoggerを取得
         try {
             this.logger = createServiceLogger('ViewManager');
-        } catch (_error) {
+        } catch {
             // フォールバック: ServiceLocatorが初期化されていない場合
             // 基本のLoggerインスタンスを作成
             this.logger = Logger.getLogger('ViewManager');
diff --git a/src/plugin/VoiceInputPlugin.ts b/src/plugin/VoiceInputPlugin.ts
index 3ec3614..17ac668 100644
--- a/src/plugin/VoiceInputPlugin.ts
+++ b/src/plugin/VoiceInputPlugin.ts
@@ -11,6 +11,14 @@ import { serviceLocator, ServiceKeys, getI18nService } from '../services';
 import { getObsidianLocale } from '../types';
 import { SafeStorageService } from '../security';
 
+type LegacyVoiceInputSettings = Partial<VoiceInputSettings> & {
+    language?: string;
+    interfaceLanguage?: string;
+    recordingMode?: string;
+    autoStopSilenceDuration?: number;
+    minSpeechDuration?: number;
+};
+
 export default class VoiceInputPlugin extends Plugin {
     settings: VoiceInputSettings;
     private viewManager: ViewManager;
@@ -110,7 +118,7 @@ export default class VoiceInputPlugin extends Plugin {
             // Add ribbon icon
             this.addRibbonIcon('microphone', i18n.t('ui.titles.main'), () => {
                 this.logger.debug('Ribbon icon clicked');
-                this.viewManager.activateVoiceInputView();
+                void this.viewManager.activateVoiceInputView();
             });
             this.logger.debug('Ribbon icon added');
 
@@ -120,7 +128,7 @@ export default class VoiceInputPlugin extends Plugin {
                 name: i18n.t('ui.commands.openView'),
                 callback: () => {
                     this.logger.debug('Command executed: open-view');
-                    this.viewManager.activateVoiceInputView();
+                    void this.viewManager.activateVoiceInputView();
                 }
             });
             this.logger.debug('Commands registered');
@@ -212,7 +220,7 @@ export default class VoiceInputPlugin extends Plugin {
     }
 
     async loadSettings() {
-        const data = await this.loadData();
+        const data = this.parseStoredSettings(await this.loadData());
 
         // まずデフォルト設定から開始
         this.settings = { ...DEFAULT_SETTINGS };
@@ -475,4 +483,11 @@ export default class VoiceInputPlugin extends Plugin {
     getLogger(): Logger | null {
         return this.logger;
     }
+
+    private parseStoredSettings(data: unknown): LegacyVoiceInputSettings | null {
+        if (typeof data === 'object' && data !== null) {
+            return data as LegacyVoiceInputSettings;
+        }
+        return null;
+    }
 }
diff --git a/src/security/SafeStorageService.ts b/src/security/SafeStorageService.ts
index 0128375..981dd2e 100644
--- a/src/security/SafeStorageService.ts
+++ b/src/security/SafeStorageService.ts
@@ -34,6 +34,16 @@ const isElectronWindow = (win: Window): win is ElectronWindow => {
     return 'require' in win && typeof (win as ElectronWindow).require === 'function';
 };
 
+const resolveElectronRenderer = (): ElectronRenderer | null => {
+    if (isElectronWindow(window) && typeof (window as ElectronWindow).require === 'function') {
+        return (window as ElectronWindow).require('electron') ?? null;
+    }
+    if ((window as ElectronWindow).electron) {
+        return (window as ElectronWindow).electron ?? null;
+    }
+    return (globalThis as ElectronGlobal).electron ?? null;
+};
+
 export class SafeStorageService {
     private static safeStorage: ElectronSafeStorage | null = null;
     private static logger: Logger = getLogger('SafeStorageService');
@@ -53,15 +63,10 @@ export class SafeStorageService {
                 this.logger.debug(`window.require exists: ${'require' in window}`);
                 this.logger.debug(`window.require is function: ${typeof (window as ElectronWindow).require === 'function'}`);
 
-                const electron = isElectronWindow(window) ? window.require?.('electron') : null;
+                const electron = resolveElectronRenderer();
 
                 if (!electron) {
-                    // Alternative access method
-                    const globalElectron = (window as ElectronWindow).electron || (global as ElectronGlobal).electron;
-                    if (globalElectron) {
-                        this.logger.debug('Found electron via global access');
-                        this.safeStorage = globalElectron.remote?.safeStorage || globalElectron.safeStorage || null;
-                    }
+                    this.logger.debug('Electron renderer not available');
                 } else {
                     this.logger.debug(`Electron object exists: ${!!electron}`);
                     this.logger.debug(`Electron.remote exists: ${!!electron?.remote}`);
diff --git a/src/services/I18nService.ts b/src/services/I18nService.ts
index 4207fac..f550180 100644
--- a/src/services/I18nService.ts
+++ b/src/services/I18nService.ts
@@ -127,8 +127,10 @@ export class I18nServiceImpl implements I18nService {
    * Supports {paramName} syntax
    */
     private substituteParams(translation: string, params: Record<string, string | number>): string {
-        return translation.replace(/{(\w+)}/g, (match, paramName) => {
-            return params[paramName]?.toString() || match;
+        return translation.replace(/{(\w+)}/g, (match, captured) => {
+            const paramKey = captured as keyof typeof params;
+            const value = params[paramKey];
+            return value !== undefined ? value.toString() : match;
         });
     }
 
diff --git a/src/utils/ObsidianHttpClient.ts b/src/utils/ObsidianHttpClient.ts
index 548aaa7..cdae223 100644
--- a/src/utils/ObsidianHttpClient.ts
+++ b/src/utils/ObsidianHttpClient.ts
@@ -20,7 +20,8 @@ export class ObsidianHttpClient {
     }): Promise<{ status: number; json: unknown; text: string }> {
         const { url, method = 'GET', headers = {}, body } = opts;
         const res = await requestUrl({ url, method, headers, body, throw: false });
-        return { status: res.status, json: res.json, text: res.text };
+        const jsonBody: unknown = res.json;
+        return { status: res.status, json: jsonBody, text: res.text };
     }
 
     /**
@@ -43,7 +44,8 @@ export class ObsidianHttpClient {
             body: JSON.stringify(data),
             throw: false
         });
-        return { status: res.status, json: res.json };
+        const jsonBody: unknown = res.json;
+        return { status: res.status, json: jsonBody };
     }
 
     /**
@@ -63,8 +65,8 @@ export class ObsidianHttpClient {
             body,
             throw: false
         });
-
-        return { status: response.status, json: response.json };
+        const jsonBody: unknown = response.json;
+        return { status: response.status, json: jsonBody };
     }
 
     /**
diff --git a/src/views/VoiceInputViewUI.ts b/src/views/VoiceInputViewUI.ts
index 4fb29ef..d00560d 100644
--- a/src/views/VoiceInputViewUI.ts
+++ b/src/views/VoiceInputViewUI.ts
@@ -33,8 +33,8 @@ export class VoiceInputViewUI {
     secondRowContainer: HTMLElement;
 
     // Settings controls
-    correctionToggle: ToggleComponent;
-    transcriptionModelDropdown: DropdownComponent;
+    correctionToggle: ToggleComponent | null = null;
+    transcriptionModelDropdown: DropdownComponent | null = null;
 
     // Event handlers
     private clickHandler: ((e: MouseEvent) => void) | null = null;