Cheerful Amnesia, Vol. 1 — Oku Tamamushi

When Arisa loses her memories from the past three years, her girlfriend, Mari, worries it might mean the end of their budding relationship. A needless concern, it turns out, because when Arisa lays eyes on her, she falls in love all over again! Arisa's not about to let a little severe brain damage get her down, because she has a chance to relive all their firsts for a second time -- from dates, to kisses, and even beyond…!!