The Ninja Who is Too Complicated

Rattled by his loss to Saitama, Sonic cannot fight properly and is plagued by recurring nightmares and flashbacks of the defeat. He takes up training in a forest alongside a Matagi hunter who is determined to slay a bear that once wounded him. Mulling over the hunter's advice, Sonic is interrupted by a noise and rushes to rescue a baby boar from a snake. The creature, which he names Ino, quickly attaches itself to him, and as his training continues, Sonic steadily rebuilds his confidence and pushes past his fears.

When Sonic prepares to leave, the hunter corrects his farewell by finally sharing his real name, Frank, catching the ninja off guard. Soon after Sonic departs, the very bear that scarred Frank ambushes and overpowers him, knocking him out. Saitama then wanders in searching for food, eyes Ino, and ends up taking the bear instead when the boar bolts. Later, at the apartment, Saitama and Genos enjoy a hot pot made with bear meat while Sonic quietly surveys the city, primed for his next clash with Saitama. When Frank comes to, he and Ino stare in astonishment at a swath of forest leveled by a single punch.

Sonic isolates himself in the forest to recover from his defeat and trains under the Matagi hunter Frank, rescuing and befriending a boar he names Ino. He regains his fighting spirit and departs. The bear ambushes Frank, but Saitama arrives, takes the bear, and shares it as hot pot with Genos, leaving Frank and Ino stunned by the destruction of a single punch.

The OVA works as a character study focused on Sonic's recovery and his growing obsession with defeating Saitama. It is positioned between the entries titled The Pupil Who Is An Extremely Poor Talker and Bang, Who Is Too Overbearing in the anime's supplementary lineup.