Dandadan. Volume 1: Yukinobu Tatsu

A nerd must fight powerful spirits and aliens all vying for the secret power of his “family jewel,” so who better to fight alongside him than his high school crush and a spirit granny?!
Momo Ayase and Okarun are on opposite sides of the paranormal spectrum regarding what they’ll believe in and what they won’t. Their quest to prove each other wrong leads them down a path of secret crushes and paranormal battles they’ll have to participate in to believe!
Momo Ayase strikes up an unusual friendship with her school’s UFO fanatic, whom she nicknames “Okarun” because he has a name that is not to be said aloud. While Momo believes in spirits, she thinks aliens are nothing but nonsense. Her new friend, meanwhile, thinks the exact opposite. To settle matters, the two set out to prove each other wrong—Momo to a UFO hotspot and Okarun to a haunted tunnel! What unfolds next is a beautiful story of young love…and oddly horny aliens and spirits?