Sorairo Kaigan

Tomo is a highschool girl who lives in a town by a beach. One day she gets harassed on a bus, but is rescued by one of her classmates. Afterwards, he drops his keys, and the key ring has the same stone as one given to Tomo by a boy during her childhood. Is he the same person? Tomo believes the sea can bestow treasures on people, and she may about to be proven right in ways she couldn't imagine.

(Source: Tokyopop)