Dandadan. Volume 6: 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!
The Kito clan tosses Okarun and the gang into an alternate-reality version of Jiji’s family home as an offering to the serpent god! There they encounter another of the clan’s sacrifices, a child who goes on to possess the softhearted Jiji. The two of them become the Evil Eye, who then attacks Okarun and Momo. Okarun decides to take him on alone and sends Momo back aboveground to get help. There she comes up with an ingenious plan to get rid of the giant serpent god…but can she pull it off on her own in time to save Jiji?