A soft voice {TsukkiYama, YamaTsukki}

Tsukkiyama

When Yamaguchi and Tsukishima were young, they used to play all the time. Tsukishima owned a music box that Yamaguchi loved very much, and aware of that fact, on Yamaguchi's 10th birthday, Tsukishima gave it to him as a gift. as the gentle train rides around and played its lovely song, it stuck with Yamaguchi for years to come, and without realizing, he began to hum to tune.

Now both of them 17 turning 18, Tsukishima felt nostalgic every time Yamaguchi hummed the tune, until one day he asked "Where have I heard that song before?"