Profoundly Mysterious Kick-the-Can Battle

Okarun shows up late to their meeting spot, forcing him and Momo to sprint for school. She grumbles that her tardiness will saddle her with an extra lesson and reminds him she should have walked on without him. On the way she casually flicks a few stray cans off the road with her psychic powers, leaving him impressed. After arriving late and enduring her scolding, the two bicker over whose fault it is. Stung, Momo declares they will stop walking together, which catches Okarun completely off guard.

In class, a dejected Momo is startled when a thrown can smashes into the window beside her. A mandrill marvels that she deflected his strike, baffled that anyone could outdo a creature of his supposed 300 IQ. Spotting the darkness outside, Momo pegs him as an alien. He knocks her through the window with another can, but she catches the ledge and lands safely, then blocks his follow-up barrage while demanding he stop littering. A giant can sits atop the building, and Okarun flees a mob of can-people, warning that the cans convert anyone they touch. The Mandrill Alien explains his Territory Can blankets a hundred-kilometer radius and reveals his plan to dissect every human turned into a can, slyly cautioning them not to destroy the fragile device.

Okarun cannot transform, blaming the Can's range, so Momo races to the roof to kick it. The alien shouts a warning, and Okarun, believing him, throws himself between Momo and the device, only to touch it and become a walking can himself. Momo leaps to safety and realizes the Can is a trap built to convert anyone who tries to break it. The mandrill, disappointed she did not transform, praises her cleverness and grows eager to dissect her. Momo fires back that he is the real monkey, boasting an IQ of three million, and holds her shield against his can storm even as her hands bleed. The classroom then begins to crumble: she had baited him into smashing the pillar supporting the Territory Can, letting gravity topple it. As the mandrill lunges with his staff, Okarun, restored to his Turbo Granny form, launches himself and knocks the alien clear out of the building. With the enemy beaten, the cans revert to confused students.

Walking home, Momo tells Okarun to keep his distance, still sore. He apologizes and presents her with a special-edition Golgo 13 DVD she had wanted, confessing he took a morning newspaper job to afford it and kept it secret. Touched, Momo agrees they can walk together again and offers her own apology for losing her temper.

A morning argument leads Momo to swear off walking to school with Okarun. The Mandrill Alien traps the school inside Empty Space with his Territory Can. Okarun is turned into a can after touching the device to protect Momo. Momo tricks the alien into destroying the pillar holding up the Can, collapsing it through gravity, and a restored Okarun knocks the mandrill out. The two reconcile, with Okarun gifting Momo a coveted DVD bought with his secret newspaper job.

This thirty-one-page one-shot was published October 3, 2021 and is collected in Volume 5. It functions as a self-contained story rather than part of the main serialized arc, pairing a lighthearted lovers' quarrel with a high-stakes alien encounter.