Hajimemashite, Watashi no Usotsuki Kareshi-kun?: Hoshigaru Tokoro, Oshiete Ageyou ka

Michika Sato is a plain, hard-working businesswoman. She's never been great with guys, and before she knows it, she's 25 and has no experience with romance... At least, that's what she remembers before hitting her head, but when she wakes up, Michika's sweet college-aged boyfriend is by her side. She has no memories of Tairi Sato, the man claiming to be her boyfriend, but even her mother seems to know and trust him. Tairi encourages Michika to take her time remembering, and as he makes love to her so gently, she can't help but wonder why he's the only person she has no memory of...

(Source: Renta!)