0 Second Proposal: My Friend's Brother Asked to Marry Me

After meeting for 0 seconds, a proposal!? One night Hana Kayama opens her door to a strange young man standing there, Keito Mikita. Moreover, he plainly proposes to her saying "May we please live together, as a married couple?" Hana thinks it's super suspicious, but it turns out he's actually the younger brother of an old friend! She wonders if the proposal is true or not, but for some reason, she can't abandon this man without a home, so they start living together!! This is a reunion with a boy who turned into a man, but what should this grown woman do with his 10 years of "true love"!?