Dandadan. Volume 2: 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!
Okarun, a high school boy obsessed with supernatural phenomena, is cursed by Turbo Granny! To break the curse, Okarun and his classmate Momo Ayase challenge Turbo Granny to a high-stakes race. But Turbo Granny’s assassin, a bound spirit in the form of a giant crab, has other plans!