yen

<div id="app">
  <p><input type="number" v-model="num"></p>
  <p>{{ num | yen }}</p>
</div>

new Vue({
  el: '#app',
  data: {
    num: 1000000
  },
  filters: {
    yen(value) {
      if (!value) return ''
      value = value.toString()
      return '\u00a5' + value
    }
  }
})