Akarui Kioku Soushitsu

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…!!
(Source: Yen Press)
Note: Chapter count includes 3 extras.