[Sterling01]

It just the Novelization of Daybreak

Spoiler for taken from Wikipedia:

One day, Rena accidentally swallows something in her mouth during her usual treasure hunting. According to Rika, the seal of the sacred "Fuwarazu Magatama" pairs were broken and Rena must've accidentally swallowed one of them. The magatama holds mysterious magical powers in which a person that has the red magatama will blindly fall in love with anyone with the white magatama.