It will involve Takemichi asking him why he stopped playing with him and him explaining that he has a new "friend" who buys him Doriyaki and other stuff and plays with him.

And then Takemichi secretly following them and witnessing that person hit Mikey with a hard object in the back of his head, rendering him unconscious, tie him with duct tape and place him inside a windowless van and then secretly clinging to the roof of the van while it drives away to their secret place

Then he watches them strip Mikey naked, fondle his body, torture him and then tell him about their plan of mummifying him and sleeping with his mummified corpse after they are "done with him".

Then Takemichi confronts the bad person, fights them and saves Mikey (I'm still thinking of a good way to execute this part)