Kanojo ni Uwaki Sareteita Ore ga, Koakuma na Kouhai ni Natsukareteimasu

A few days before Christmas, college sophomore Hasegawa Yuuta learns that his girlfriend has been cheating on him. Dejected and alone, he's evading all the happy couples celebrating the festive season when he suddenly bumps into Shinohara Mayu, a beautiful girl in a Santa outfit. It doesn't take long for her to start finding the fun in teasing her gloomy senpai, and soon, she's finding any excuse to spend time with him. What began as a miserable start to the holiday season is quickly becoming a Christmas worth remembering!

(Source: Seven Seas Entertainment)