Yamaguchi and Yachi are dating and Tsukishima thought he was ok with it. Then he suddenly starts to cough and vomit flower petals which are a sign of one-sided love. He doesn't have the money to get the flowers in his throat removed so his only option to tell Yamaguchi how he feels. If he doesn't tell him the flowers will continue to grow and Tsukishima will die.

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.