Eve of the 12 Months

Winter─ A time of year where people feel the need to run around every waking moment with a deluge of feelings in their hearts. The scenery in a new development near the urban center, Megumi City, only made that sentiment more prominent. Then, on Christmas Eve─

An utterly unremarkable young man runs into a mysterious girl while out on an errand. It is when he realizes this girl he has no memory of ever meeting is, for some reason, familiar to him that their story begins...

─One wishes to protect the fun times they share.
─Another has something to gain.
─The last is determined to accomplish their goal.

Each of their fates interleave into a tale.

[From MangaGamer]