Sweet Potatoes

Have you heard of the mystery of The Lost Boy Of The Kitchen?
Rumors state that if you go into the school kitchen alone after school, you'll find on the counter a random freshly made meal. And next to it a small folded square of paper, on which a letter is scrawled in lopsided handwriting. A letter to someone the Lost Boy is looking for, and has been looking for without fail for more than a decade, the letter always starting with the same four words.
"I had a brother."

Or

Teru gets a letter from his dead brother.

Cross posted on Ao3