Flower Man

From Wataame Shoujo:

It’s a story about a girl who seeks revenge against the guy who’s ads made her want to transfer dorm which later got burned down while at the same time her cellphone and wallet got stolen! She finally got him to compensate by being her maid/servant?!

A girl received a flower which bloomed into a boy. The boy grew really quickly, to the point that he is now the same age as her…And guess who fell in love with him?
But their relationship somehow become mother/servant.