Sign language. The first time Tsukishima decided to put effort into something.

Yamaguchi has to put up with a mental mother on his own. Tsukishima tries to push through and get yamaguchi to trust him but does yamaguchi let him?

i would die for you, a thousand times over

Tsukishima and Yamaguchi are both in the YouTube industry. Eventually, these two come to find each other's channel and begin to form a friendship.