diff --git a/src/backend/src/db/migration.rs b/src/backend/src/db/migration.rs
new file mode 100644
index 0000000..6f85d2e
--- /dev/null
+++ b/src/backend/src/db/migration.rs
@@ -0,0 +1,127 @@
+use sqlx::SqlitePool;
+use sqlx::Row;
+
+/// 全てのマイグレーションを実行する
+pub async fn run_migrations(pool: &SqlitePool) -> Result<(), String> {
+    // v0.2.5 -> v0.3.0
+    migrate_025_to_030(pool).await?;
+    
+    // 今後、バージョンが増えるごとにここに追加
+    // migrate_030_to_040(pool).await?;
+
+    Ok(())
+}
+
+async fn migrate_025_to_030(pool: &SqlitePool) -> Result<(), String> {
+    // 1. internal_metadata テーブルが存在するか確認
+    let row = sqlx::query("SELECT 1 FROM sqlite_master WHERE type='table' AND name='internal_metadata'")
+        .fetch_optional(pool)
+        .await
+        .map_err(|e| e.to_string())?;
+
+    if row.is_some() {
+        // すでにメタデータテーブルがある場合は、0.3.0以降とみなす
+        return Ok(());
+    }
+
+    // 2. items テーブルの構造を確認（v0.2.5以前の判定）
+    let rows = sqlx::query("PRAGMA table_info(items)")
+        .fetch_all(pool)
+        .await
+        .map_err(|e| e.to_string())?;
+
+    if rows.is_empty() {
+        // テーブル自体がない（新規導入）の場合はマイグレーション不要
+        return Ok(());
+    }
+
+    let has_path = rows.iter().any(|row| {
+        let name: String = row.get(1);
+        name == "path"
+    });
+
+    if !has_path {
+        return Ok(());
+    }
+
+    log::info!("Migrating database from v0.2.5 to v0.3.0 (Dedicated Migrator)...");
+
+    // 外部キー制約を一時的に無効化
+    sqlx::query("PRAGMA foreign_keys = OFF")
+        .execute(pool)
+        .await
+        .map_err(|e| e.to_string())?;
+
+    let mut tx = pool.begin().await.map_err(|e| e.to_string())?;
+
+    // documents テーブルを作成
+    sqlx::query(
+        "CREATE TABLE IF NOT EXISTS documents (
+            id INTEGER PRIMARY KEY AUTOINCREMENT,
+            path TEXT UNIQUE,
+            mime TEXT,
+            created_at TEXT DEFAULT (datetime('now', 'localtime')),
+            updated_at TEXT DEFAULT (datetime('now', 'localtime'))
+        )",
+    )
+    .execute(&mut *tx)
+    .await
+    .map_err(|e| e.to_string())?;
+
+    sqlx::query("INSERT OR IGNORE INTO documents (path) SELECT DISTINCT path FROM items")
+        .execute(&mut *tx)
+        .await
+        .map_err(|e| e.to_string())?;
+
+    sqlx::query(
+        "CREATE TABLE items_new (
+            id INTEGER PRIMARY KEY AUTOINCREMENT,
+            document_id INTEGER NOT NULL,
+            chunk_index INTEGER NOT NULL,
+            content TEXT NOT NULL,
+            created_at TEXT,
+            updated_at TEXT,
+            FOREIGN KEY(document_id) REFERENCES documents(id) ON DELETE CASCADE
+        )",
+    )
+    .execute(&mut *tx)
+    .await
+    .map_err(|e| e.to_string())?;
+
+    sqlx::query(
+        "INSERT INTO items_new (id, document_id, chunk_index, content, created_at, updated_at)
+         SELECT 
+            i.id, 
+            d.id, 
+            (SELECT COUNT(*) FROM items i2 WHERE i2.path = i.path AND i2.id < i.id),
+            i.content, 
+            i.created_at, 
+            i.updated_at
+         FROM items i
+         JOIN documents d ON i.path = d.path",
+    )
+    .execute(&mut *tx)
+    .await
+    .map_err(|e| e.to_string())?;
+
+    sqlx::query("DROP TABLE items")
+        .execute(&mut *tx)
+        .await
+        .map_err(|e| e.to_string())?;
+
+    sqlx::query("ALTER TABLE items_new RENAME TO items")
+        .execute(&mut *tx)
+        .await
+        .map_err(|e| e.to_string())?;
+
+    tx.commit().await.map_err(|e| e.to_string())?;
+
+    sqlx::query("PRAGMA foreign_keys = ON")
+        .execute(pool)
+        .await
+        .map_err(|e| e.to_string())?;
+
+    log::info!("Migration v0.2.5 to v0.3.0 completed successfully.");
+
+    Ok(())
+}
diff --git a/src/backend/src/db/mod.rs b/src/backend/src/db/mod.rs
new file mode 100644
index 0000000..e46af45
--- /dev/null
+++ b/src/backend/src/db/mod.rs
@@ -0,0 +1,355 @@
+use sqlx::Row;
+use sqlx::SqlitePool;
+use sqlx::sqlite::{SqliteConnectOptions, SqlitePoolOptions};
+use std::borrow::Cow;
+use std::path::Path;
+use std::str::FromStr;
+
+pub mod migration;
+
+/// データベースを初期化し、コネクションプールを返す。
+/// 埋め込み次元が変更されている場合は vec_items テーブルを再作成する。
+pub async fn initialize_database(
+    db_path: &Path,
+    extension_path: &Path,
+    dimension: usize,
+) -> Result<SqlitePool, String> {
+    // ディレクトリの作成
+    if let Some(parent) = db_path.parent() {
+        if !parent.exists() {
+            std::fs::create_dir_all(parent).map_err(|e| e.to_string())?;
+        }
+    }
+
+    let db_path_str = db_path.to_str().ok_or("Invalid DB path")?;
+    let ext_path_str = extension_path.to_str().ok_or("Invalid extension path")?;
+
+    let opts = SqliteConnectOptions::from_str(&format!("sqlite://{}?mode=rwc", db_path_str))
+        .map_err(|e| e.to_string())?
+        .extension(ext_path_str.to_owned());
+
+    let pool = SqlitePoolOptions::new()
+        .max_connections(5)
+        .connect_with(opts)
+        .await
+        .map_err(|e| e.to_string())?;
+
+    // スキーマ初期化
+    init_schema(&pool, dimension).await?;
+
+    Ok(pool)
+}
+
+async fn init_schema(pool: &SqlitePool, dimension: usize) -> Result<(), String> {
+    // PRAGMA設定
+    sqlx::query("PRAGMA journal_mode = WAL")
+        .execute(pool)
+        .await
+        .map_err(|e| e.to_string())?;
+
+    // マイグレーションの実行
+    migration::run_migrations(pool).await?;
+
+    // 内部管理（バージョン等）テーブル
+    sqlx::query(
+        "CREATE TABLE IF NOT EXISTS internal_metadata (
+            key TEXT PRIMARY KEY,
+            value TEXT
+        )",
+    )
+    .execute(pool)
+    .await
+    .map_err(|e| e.to_string())?;
+
+    // バージョン情報の書き込み (0.3.0)
+    sqlx::query("INSERT OR REPLACE INTO internal_metadata (key, value) VALUES ('version', '0.3.0')")
+        .execute(pool)
+        .await
+        .map_err(|e| e.to_string())?;
+
+    // ドキュメント（親メタデータ）テーブル
+    sqlx::query(
+        "CREATE TABLE IF NOT EXISTS documents (
+            id INTEGER PRIMARY KEY AUTOINCREMENT,
+            path TEXT UNIQUE,
+            mime TEXT,
+            created_at TEXT DEFAULT (datetime('now', 'localtime')),
+            updated_at TEXT DEFAULT (datetime('now', 'localtime'))
+        )",
+    )
+    .execute(pool)
+    .await
+    .map_err(|e| e.to_string())?;
+
+    // アイテム（チャンク）テーブル
+    sqlx::query(
+        "CREATE TABLE IF NOT EXISTS items (
+            id INTEGER PRIMARY KEY AUTOINCREMENT,
+            document_id INTEGER NOT NULL,
+            chunk_index INTEGER NOT NULL,
+            content TEXT NOT NULL,
+            created_at TEXT DEFAULT (datetime('now', 'localtime')),
+            updated_at TEXT DEFAULT (datetime('now', 'localtime')),
+            FOREIGN KEY(document_id) REFERENCES documents(id) ON DELETE CASCADE
+        )",
+    )
+    .execute(pool)
+    .await
+    .map_err(|e| e.to_string())?;
+
+    // LSA ベクトル保存テーブル (意味検索用)
+    sqlx::query(
+        "CREATE TABLE IF NOT EXISTS items_lsa (
+            id INTEGER PRIMARY KEY,
+            vector BLOB NOT NULL,
+            FOREIGN KEY(id) REFERENCES items(id) ON DELETE CASCADE
+        )",
+    )
+    .execute(pool)
+    .await
+    .map_err(|e| e.to_string())?;
+
+    // トリガー作成 (documents)
+    sqlx::query(
+        "CREATE TRIGGER IF NOT EXISTS update_documents_updated_at
+        AFTER UPDATE ON documents
+        FOR EACH ROW
+        BEGIN
+            UPDATE documents SET updated_at = datetime('now', 'localtime') WHERE id = OLD.id;
+        END",
+    )
+    .execute(pool)
+    .await
+    .map_err(|e| e.to_string())?;
+
+    // トリガー作成 (items)
+    sqlx::query(
+        "CREATE TRIGGER IF NOT EXISTS update_items_updated_at
+        AFTER UPDATE ON items
+        FOR EACH ROW
+        BEGIN
+            UPDATE items SET updated_at = datetime('now', 'localtime') WHERE id = OLD.id;
+        END",
+    )
+    .execute(pool)
+    .await
+    .map_err(|e| e.to_string())?;
+
+    // vec_items の次元数チェックと初期化
+    check_and_init_vector_table(pool, dimension).await?;
+
+    Ok(())
+}
+
+
+async fn check_and_init_vector_table(pool: &SqlitePool, dimension: usize) -> Result<(), String> {
+    // 現在のテーブル定義を確認
+    let row = sqlx::query("SELECT sql FROM sqlite_master WHERE type='table' AND name='vec_items'")
+        .fetch_optional(pool)
+        .await
+        .map_err(|e| e.to_string())?;
+
+    let should_recreate = if let Some(row) = row {
+        let sql: String = row.get(0);
+        // "FLOAT[640]" のような文字列が含まれているかチェック
+        let expected = format!("FLOAT[{}]", dimension);
+        if !sql.contains(&expected) {
+            log::info!("Dimension mismatch detected (expected {}). Rebuilding vec_items...", dimension);
+            true
+        } else {
+            false
+        }
+    } else {
+        true
+    };
+
+    if should_recreate {
+        let mut tx = pool.begin().await.map_err(|e| e.to_string())?;
+
+        sqlx::query("DROP TABLE IF EXISTS vec_items")
+            .execute(&mut *tx)
+            .await
+            .map_err(|e| e.to_string())?;
+
+        let create_sql = format!(
+            "CREATE VIRTUAL TABLE vec_items USING vec0(id INTEGER PRIMARY KEY, embedding FLOAT[{}])",
+            dimension
+        );
+        sqlx::query(&create_sql)
+            .execute(&mut *tx)
+            .await
+            .map_err(|e| e.to_string())?;
+
+        // 既存の items があればベクトルを再生成する必要があるが、
+        // ここでは空のテーブル作成に留める。
+        // （/v1/embeddings が必要になるため、再生成は別のユーティリティで行うのが安全）
+
+        tx.commit().await.map_err(|e| e.to_string())?;
+    }
+
+    Ok(())
+}
+
+/// 全データのベクトルを再生成する
+pub async fn rebuild_vector_data<F, Fut>(
+    pool: &SqlitePool,
+    dimension: usize,
+    embed_fn: F,
+) -> Result<(), String> 
+where 
+    F: Fn(String) -> Fut,
+    Fut: std::future::Future<Output = Result<Vec<f32>, String>>,
+{
+    // 強制的に再作成
+    {
+        let mut tx = pool.begin().await.map_err(|e| e.to_string())?;
+        sqlx::query("DROP TABLE IF EXISTS vec_items")
+            .execute(&mut *tx)
+            .await
+            .map_err(|e| e.to_string())?;
+        let create_sql = format!(
+            "CREATE VIRTUAL TABLE vec_items USING vec0(id INTEGER PRIMARY KEY, embedding FLOAT[{}])",
+            dimension
+        );
+        sqlx::query(&create_sql)
+            .execute(&mut *tx)
+            .await
+            .map_err(|e| e.to_string())?;
+        tx.commit().await.map_err(|e| e.to_string())?;
+    }
+
+    let rows = sqlx::query("SELECT id, content FROM items")
+        .fetch_all(pool)
+        .await
+        .map_err(|e| e.to_string())?;
+
+    for row in rows {
+        let id: i64 = row.get("id");
+        let content: String = row.get("content");
+        let emb = embed_fn(content).await?;
+        
+        sqlx::query("INSERT INTO vec_items (id, embedding) VALUES (?, ?)")
+            .bind(id)
+            .bind(serde_json::to_string(&emb).unwrap_or_default())
+            .execute(pool)
+            .await
+            .map_err(|e| e.to_string())?;
+    }
+
+    Ok(())
+}
+
+/// itemsテーブルにあってvec_itemsテーブルにないデータを同期する（ヒーリング）
+pub async fn sync_vectors<F, Fut>(
+    pool: &SqlitePool,
+    embed_fn: F,
+) -> Result<usize, String>
+where
+    F: Fn(String) -> Fut,
+    Fut: std::future::Future<Output = Result<Vec<f32>, String>>,
+{
+    // vec_itemsに存在しないIDを抽出
+    let rows = sqlx::query(
+        "SELECT i.id, i.content 
+         FROM items i 
+         LEFT JOIN vec_items v ON i.id = v.id 
+         WHERE v.id IS NULL"
+    )
+    .fetch_all(pool)
+    .await
+    .map_err(|e| e.to_string())?;
+
+    let count = rows.len();
+    if count == 0 {
+        return Ok(0);
+    }
+
+    log::info!("Healing {} missing vectors...", count);
+
+    for row in rows {
+        let id: i64 = row.get("id");
+        let content: String = row.get("content");
+        
+        match embed_fn(content).await {
+            Ok(emb) => {
+                sqlx::query("INSERT INTO vec_items (id, embedding) VALUES (?, ?)")
+                    .bind(id)
+                    .bind(serde_json::to_string(&emb).unwrap_or_default())
+                    .execute(pool)
+                    .await
+                    .map_err(|e| e.to_string())?;
+            }
+            Err(e) => {
+                log::error!("Failed to generate embedding for item {}: {}", id, e);
+            }
+        }
+    }
+
+    Ok(count)
+}
+
+// 下位互換性（既存の依存箇所が多いため、一時的に定義を残すか、順次書き換える）
+pub async fn init_pool(
+    db_path: &str,
+    extension_path: impl Into<Cow<'static, str>>,
+) -> Result<SqlitePool, sqlx::Error> {
+    let opts = SqliteConnectOptions::from_str(&format!("sqlite://{}?mode=rwc", db_path))?
+        .extension(extension_path);
+
+    SqlitePoolOptions::new().connect_with(opts).await
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    // use std::fs;
+    use tempfile::tempdir;
+
+    #[tokio::test]
+    async fn test_dimension_change_and_rebuild() {
+        let dir = tempdir().unwrap();
+        let db_path = dir.path().join("test_telos.db");
+        
+        // DLLのパス取得（ビルドディレクトリにあることが前提）
+        // テスト環境では $OUT_DIR や $CARGO_MANIFEST_DIR 基準で探す
+        let manifest_dir = env!("CARGO_MANIFEST_DIR");
+        let ext_path = Path::new(manifest_dir).join("../node_modules/sqlite-vec-windows-x64/vec0.dll");
+
+        if !ext_path.exists() {
+            println!("Skipping test: vec0.dll not found at {:?}", ext_path);
+            return;
+        }
+
+        // 1. 最初は次元数 384 で初期化
+        let pool = initialize_database(&db_path, &ext_path, 384).await.unwrap();
+        
+        // テーブル定義の確認
+        let row: (String,) = sqlx::query_as("SELECT sql FROM sqlite_master WHERE name='vec_items'")
+            .fetch_one(&pool).await.unwrap();
+        assert!(row.0.contains("FLOAT[384]"));
+        
+        // データ挿入
+        let doc_id = sqlx::query("INSERT INTO documents (path) VALUES ('test_path')")
+            .execute(&pool).await.unwrap().last_insert_rowid();
+        sqlx::query("INSERT INTO items (document_id, chunk_index, content) VALUES (?, ?, ?)")
+            .bind(doc_id)
+            .bind(0)
+            .bind("test content")
+            .execute(&pool).await.unwrap();
+        
+        pool.close().await;
+
+        // 2. 次は次元数 768 で再初期化（不整合検知 -> 再作成）
+        let pool2 = initialize_database(&db_path, &ext_path, 768).await.unwrap();
+        let row2: (String,) = sqlx::query_as("SELECT sql FROM sqlite_master WHERE name='vec_items'")
+            .fetch_one(&pool2).await.unwrap();
+        assert!(row2.0.contains("FLOAT[768]"));
+
+        // items テーブルは維持されていることを確認
+        let count: (i64,) = sqlx::query_as("SELECT COUNT(*) FROM items")
+            .fetch_one(&pool2).await.unwrap();
+        assert_eq!(count.0, 1);
+        
+        pool2.close().await;
+    }
+}