Please Teacher!

おねがい☆ティーチャー

Kei Kusanagi looks fifteen but is older, having lost years to a coma-like "standstill" triggered by emotional shock. One night he watches a woman descend from the sky; the next day she joins his school as the new teacher Mizuho Kazami, secretly a half-alien observer sent to study Earth. When a misunderstanding forces them into a hidden marriage, Kei and Mizuho try to keep the arrangement secret from classmates and family alike.