From Summer-Rain:
Between three highschool students, a secret love affair begins..

Straight-A student Yuka is a little too honest for her own good and has no friends but unexpectedly begins dating Haruomi after he helps her out of a difficult situation. The only problem is, Haruomi has a strict policy of dating someone new every Monday…

(Source: Tokyo Otaku Mode)

Included one-shot:
Volume 2: Hatsu Date (A First Date)

A short story of a reindeer who becomes human in order to find the boy who called her "pretty" five years ago.
(Source: MU)