During his usual Tae stakeouts, Kondou meets a mysterious old man who is determined to teach the Shinsengumi Commander the ways of a thief so he can take over. But what is the real connection between the two men and apes?
A flashback is shown where a child Kondou is disowned by his father. Back in the present, Kondou wakes up underneath the Shimura home's floorboards and with athletic stealth and agility, jumps to the roof. He is complemented on by a mysterious old man who decides that Kondou would be perfect to be his successor, to Kondou's shock. The next day, the Shinsengumi investigates a robbery of a loan shark; Hijikata asked the Commander about his whereabouts before telling him about the famous Robin Hood-like thief named Etekichi Kozou (Ape Boy), who steals money from extorting criminals and gives back to the poor by showering bananas. Hijikata admits the monkey-like thief was doing a good deed, but he's still a thief and disrespecting the police so needs to be caught. Kondou agrees, as the scene cuts to a few days later at night while he trains with the thief catching monkeys' tails in a zoo. Kozou expresses his pride in Kondou's growth but before Kondou can tell the old man that he was actually a cop, the Shinsengumi, lead by Hijikata, arrives, investigating reports on illegal entries. The two men were able to escape, greatly helped by Kondou accidentally hurting Hijikata, but the old man collapses. Resting in a rundown shack, Kozou reveals that he was desperately looking for a successor because he didn't have long to live. He asks Kondou to continue his legacy including giving offerings to a particular shrine.
The next day at the shrine, Kondou encounters an injured Hijikata who tells him that he knew the mysterious men last night was the thief and Kondou and was keeping his temper at his superior hurting him in check, believing this to be an 'undercover operation'; Kondou emphatically 'agrees'. An old lady appears and tells the cops that someone has been leaving bananas and money as offerings to the shrine, restoring it. The shrine was once larger also holding a temple school. The chief priest was a kind man who taught children, including taking in a problem child and mending his ways. Unfortunately loan sharks took advantage of the priest, took the land and kidnapped a few children. The problem child and a few other kids rescued the children and the deed to the shrine's lands. In retaliation the loan sharks burned down the shrine and the problem child was never seen again. Hijikata believes that the problem child was the thief, but Kondou corrects him, stating that the child was himself. He was a problem child due to his primate-like behavior. The Shinsengumi commander also reveals that the old lady was his classmate and Kozou was the chief priest.
It turns out that after the shrine was burned down, the saddened priest tells the children to not tell young Kondou (injured and unconscious being taken care of by his father) about this and blames himself for his failures, also disappearing. Hijikata concludes that the priest became a thief to help protect his beloved shrine; Kondou adds the priest protected Kondou, too (young Kondou decides to no longer visit the shrine, in return he will vigorously train under his father to become stronger). Hijikata then gets a call about another robbery; when the police get there it was empty. The Vice-Chief realizes that the yakuza is also after thief; Kondou finding Kozou's handkerchief shows that the thugs caught him first. Badly beaten, Kozou is surrounded by thugs who plan on killing him. They are interrupted by Kondou's arrival and he defeats almost every one of them before Hijikata and the rest arrives. The Commander tries to help Kozou, who reveals that he knew who Kondou was the entire time and was proud of him before dying. Sometime later someone leaves money and bananas as offerings at the shrine. While the students wonder who keeps leaving them, a hidden Kondou smiles at the scene and leaves.
- Kondou Isao
- Hijikata Toushirou
- Sakata Gintoki (cameo, flashback)
- Shimura Tae (cameo)
- Kondou's Father (flashback)
- Etekichi Kozou
- Kouri Hanako