Itsudatte My Santa!

An unlucky boy named Santa was born on Christmas Eve whose parents don't even care about meets a santa- in- training girl name Mai. She is determined to wish him the best Christmas he will ever have and it gets even better when they fall in love with each other.
Mai, a Santa in training, appears in front of an unlucky boy named Santa, on Christmas Eve, promising him, she will make him happy for one night.
(Source: Anime News Network)