A Shadow That Snuck Up Too Close

Bridging the gap between Mosquito Girl's defeat and Genos taking up residence at Saitama's place, the OVA opens at night with Saitama watching a program about aliens and stalkers. He becomes sure he is being followed, and the culprit is revealed to be Genos, who is trying to uncover the secret behind Saitama's power. When Saitama heads out to eat, Genos trails him into a pricey restaurant, where the frugal hero orders only a small plate of fries. Convinced the food holds the key, Genos swipes the single long fry Saitama liked best for analysis while Saitama steps away, leaving the hero baffled at the theft when he returns.

Later, Saitama waits outside his building to catch his stalker, unaware Genos is observing him from a different angle. Around then a B-Class criminal, Men's Esthetician Man, launches an assault and recognizes Saitama as someone who once beat him, though Saitama has no memory of the man and instead pegs him as the fry thief. Meanwhile at Kuseno's lab, Genos reviews the results and finds nothing but an ordinary french fry, leading him to guess that Saitama might be a cyborg like himself. Back with Saitama, a hole shaped like Men's Esthetician Man is left in a wall as Saitama tells him to simply approach next time rather than steal his food. The story closes with Genos standing outside the apartment, looping back to where the main series began.

Genos secretly tails Saitama to learn the source of his strength and steals one of his fries for laboratory analysis. Saitama, sensing a stalker, mistakes the attacking Men's Esthetician Man for the culprit and defeats him. The fry proves ordinary, prompting Genos to theorize that Saitama could be a cyborg, and the OVA ends at the moment Genos arrives at Saitama's door.

The OVA is framed as a side story slotted between Mosquito Girl's defeat and Genos's introduction in the main narrative. It sits between the Road to Hero OVA and the entry titled The Pupil Who Is An Extremely Poor Talker in the anime's supplementary lineup.