When Masato is transfered to a job where he was basically waiting to be fired, but used his extra time to help disabled children (specifically autistic kids) because he wants to make Hikaru's life easier. D'awwwwwwwww.
Aoki-sensei's wedding most definitely counts: Aoki himself was reduced to tears when his students performed the Mouse March. Then, he joined them.
Kanon standing up to the kids who make fun of her and Hikaru. A true sibling standing up for her brother.
When Hikaru saw his mother crying after realizing he will not be 'normal', he gave Sachiko a few wildflowers that snapped her out of her despair.