Kin no Tamago

Kamome is an inventor, and her latest invention is a machine that will restore anyone to perfect health, which she created so her grandfather, Kinkaku, could live a long life. When Kinkaku tries to take a look at the machine, he ends up activating it and losing consiousness. When he comes to and climbs out of the machine, he finds out he's been turned into a child! After a little adventure, Kinkaku decides he must insinuate himself into Kamome's school life in order to protect her. Will Kinkaku ever return to his original body?