On your 16th birthday, you get the name of your soulmate on your arm. Tadashi Yamaguchi often scribbles and doodles on his best friend's arm. Kei Tsukishima is that best friend and he wakes up with Yamaguchi's name on his arm.
The haikyu boys have a 2 day sleepover and let's say confessions and party games are played. MANY SHIPS INCLUDED DONT MIND ME!
Tsukishima was always kind of cold to Yamaguchi but no matter what Yamaguchi couldn't help but fall in love with him. Tsukishima was always oblivious to these feelings and now everything was being changed.