This can be noticed when the group of Denji, Asa Mitaka, Fami, Yoshida, and Fumiko Mifune are seated at a cafe, ordering food. It is what Fumiko orders— an orange juice— that teases the fact ...

Denji then states that the others can leave through his mouth, meaning that only the two of them would stay in that case. Chainsaw Man chapter 190 then has a short time skip where Fumiko Mifune ...

using Denji’s mouth as a portal to return to reality, but Aging retaliates and ages her face rapidly. Pochita then cut off the devil’s head, though Aging regenerates through Fumiko’s organs.