Cheerful Amnesia, Vol. 1 (manga)

Arisa has lost her memories of the past three years, and her girlfriend Mari worries that means their love has vanished as well. But when Arisa lays eyes on her, it's love at first sight all over again! Hoping to rekindle what they had, Mari decides to help Arisa experience things with her once more, from dates, to kissing, and beyond...?!