Laravel + vue　ユーザー詳細でユーザーに紐づくtweetsが表示されない

vue-devtoolsで確認するとuserの詳細はdataとしてありvueに表示されるのですが、そのuserに紐づくtweetsがdataにありません。
宜しくお願い致します。

###vue-devtools

###User.php

<?php

namespace App;

use Illuminate\Notifications\Notifiable;
use Illuminate\Contracts\Auth\MustVerifyEmail;
use Illuminate\Foundation\Auth\User as Authenticatable;

class User extends Authenticatable
{
    use Notifiable;

    /**
     * リレーションシップ - tweetsテーブル
     * @return \Illuminate\Database\Eloquent\Relations\HasMany
     */
    public function tweets()
    {
        return $this->hasMany('App\Tweet');
    }

    /**
     * The attributes that are mass assignable.
     *
     * @var array
     */
    protected $fillable = [
        'name', 'email', 'password',
    ];

    /**
     * The attributes that should be hidden for arrays.
     *
     * @var array
     */
    protected $hidden = [
        'email_verified_at', 'password', 'remember_token',
    ];

    /**
     * The attributes that should be cast to native types.
     *
     * @var array
     */
    protected $casts = [
        'email_verified_at' => 'datetime',
    ];

    protected $visible = [
        'id', 'name', 'email', 'tweets',
    ];

}

###UserController.php

<?php

namespace App\Http\Controllers;

use App\User;
use Illuminate\Http\Request;
use Illuminate\Support\Facades\Auth;
use Illuminate\Support\Facades\DB;
use Illuminate\Support\Facades\Storage;

class UserController extends Controller
{
    public function __construct()
    {
        // 認証が必要
        $this->middleware('auth')->except(['show']);
    }

    /**
     * user詳細
     * @param string $id
     * @return User
     */
    public function show(string $id)
    {
        $user = User::where('id', $id)->with(['tweets'])->first();

        return $user ?? abort(404);
      
    }
}

###UserDetail.vue

<template>
  <div v-if="user" class="tweet-detail">
    <nav class="panel panel-default">
      <div class="list-group">
        <img src="" alt="icon" class="img-circle">
          <div class="list-group-item">
            <span>
              {{ user.name }}さん
            </span>
          </div>
      </div>
    </nav>
    <div class="tweet-list">
      <div class="grid">
        <Tweet
          class="grid__item"
          v-for="tweet in user.tweets"
          :key="tweet.id"
          :item="tweet"
          :id="tweet.id"
        />
      </div>
    </div>
  </div>
</template>

<script>
import { OK } from '../util'
import Tweet from '../components/Tweet.vue'

export default {
  components: {
    Tweet
  },
  props: {
    id: {
      type: String,
      required: true
    },
  },
  data () {
    return {
      user: null,
    }
  },
  methods: {
    async fetchUser () {
      const response = await axios.get(`/api/users/${this.id}`)

      if (response.status !== OK) {
        this.$store.commit('error/setCode', response.status)
        return false
      }

      this.user = response.data
      this.user.tweets = response.data.data
    }
  },
  watch: {
    $route: {
      async handler () {
        await this.fetchUser()
      },
      immediate: true
    }
  }
}
</script>

###Tweet.vue

<template>
  <div v-if="item" class="col">
    <nav class="panel panel-default">
      <div class="list-group">
        <img src="" alt="icon" class="img-circle">
        <RouterLink
          class="tweet__overlay"
          :to="`/users/${item.owner.id}`"
          :title="`View the user detail`"
          :item="item.owner"
        >
          <div class="list-group-item">
            <span>
              {{ item.owner.name }}さん
            </span>
          </div>
        </RouterLink>
        <RouterLink
          class="tweet__overlay"
          :to="`/tweets/${item.id}`"
          :title="`View the tweet by ${item.owner.name}`"
        >
          <div class="list-group-item">
            <span>
              {{ item.text }}
            </span>
          </div>
        </RouterLink>
        <div class="tweet__controls">
          <button
            class="tweet__action tweet__action--like"
            title="Like tweet"
          >
            <i class="icon ion-md-heart"></i>12
          </button>
        </div>
      </div>
    </nav>
  </div>
</template>

<script>
export default {
  props: {
    item: {
      type: Object,
      required: true
    },
  }
}
</script>

###api.php

<?php

use Illuminate\Http\Request;

/*
|--------------------------------------------------------------------------
| API Routes
|--------------------------------------------------------------------------
|
| Here is where you can register API routes for your application. These
| routes are loaded by the RouteServiceProvider within a group which
| is assigned the "api" middleware group. Enjoy building your API!
|
*/

// 会員登録
Route::post('/register', 'Auth\RegisterController@register')->name('register');
// ログイン
Route::post('/login', 'Auth\LoginController@login')->name('login');
// ログアウト
Route::post('/logout', 'Auth\LoginController@logout')->name('logout');
// ログインユーザー
Route::get('/user', function () {
    return Auth::user();
})->name('user');

// tweet投稿
Route::post('/tweets', 'TweetController@create')->name('tweet.create');
// tweet一覧
Route::get('/tweets', 'TweetController@index')->name('tweet.index');
// tweet詳細
Route::get('/tweets/{id}', 'TweetController@show')->name('tweet.show');

// user詳細
Route::get('/users/{id}', 'UserController@show')->name('user.show');