The O-Parts lab has been disassembeld after the DNA baby escaped, leaving more questions than answers.

Ryo Ashihara, after being distanced from his swim coach, tries to get back together with his former girlfriend Mayumi Kitahira, Mana Kazaya's new math tutor, as a way to keep him grounded as he tries to figure out what is happening to him.

After being saved by Agito from the two snake Unknowns and seeing Ryo Ashihara accidentally change into Kamen Rider Gills Mayumi Kitahira decides she must put distance between herself and her former boyfriend.

Seeing her leave Ryo decides to put his transformation to the test, but he must battle the monster within himself.