Kotonoha

When Fujita was in high school, she had but one romantic encounter - and it was with another girl. It happened one day when they ended up kissing. However, somewhere inside her, she knew a girl kissing another girl was wrong, so she chose to remain as just friends. Even when graduation came, she could not confess her feelings, and so the two girls split ways. Five years later, Fujita still thinks back to that romantic encounter. Meanwhile at work, due to one of her colleagues going on maternity leave, a new designer is brought into the company... and who does that designer turn out to be? None other than her high school crush!

(Source: MangaPlaza)