Vue

HTML

<div id="app">
  <div v-if="pair.includes('a')">
    <button @click="click('a')">A</button>
    A
  </div>

  <div v-if="pair.includes('b')">
    <button @click="click('b')">B</button>
    B
  </div>

  <div v-if="pair.includes('c')">
    <button @click="click('c')">C</button>
    C
  </div>

  <div v-if="pair.includes('d')">
    <button @click="click('d')">D</button>
    D
  </div>
</div>

Vue

new Vue({
  el: "#app",
  data () {
    return {
      clicked: "default"
    }
  },
  computed: {
    pair () {
      return {
        default: ["a", "b"],
        a: ["a", "c"],
        b: ["c", "b"],
        c: ["a", "b"]
      }[this.clicked]
    }
  },
  methods: {
  	click (clicked) {
    	this.clicked = clicked
    }
  }
})