Dandadan. Volume 12: 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!
A gravely injured Okarun wakes up to an out-of-body experience! And when he answers Momo’s phone, he’s sucked through the telephone wires to where Seiko and Turbo Granny are in the middle of a battle. Thankfully, Turbo Granny is able to teach Okarun a technique for returning to his body that will also help in the impending alien invasion. Elsewhere, Momo and the others are undergoing their own training, but when they return home on the predicted date of the invasion, they find it’s already begun!