Tiger is a character inspired by a student. He was born in the year of - no prize for guessing - and he joined the school one year later than his peers, so he's this big Tiger in the midst of a bunch of Bunnies. He is the largest boy in class, and has a big personality to match. A really good cartoonist too.
So, the bunnies' illegal experimentation with chemicals (see "Bunny Bubble Tea" Pt 1 to 3) landed them in the hospital. One bunny experiences a greater side effect than others . . .