Jakdu: Shaman's Blade

Yongjin is a struggling orphan—a blunt realist with no time or money to spare on superstitious nonsense. But on his 16th birthday, he finds his life taking a dramatic turn when his classmate Huisu, whom he had never interacted with before, suddenly asks to be his girlfriend. For the first time, Yongjin isn't alone—but his new company isn't exactly the kind he had always wished for, as he finds himself being chased by spirits instead! Though this wasn't quite the sweet sixteen he had in mind, Yongjin must now navigate through a new world he never thought existed.

(Source: Webtoon Entertainment)