Chapter 87 of the Jigokuraku manga.
During the first night they camped out on the island, Sagiri is constantly told by Gabimaru that she was feeling sleepy but denies it. She recommends that he sleep after the battles he fought but is told that he is able to keep himself awake since he is a ninja. Sagiri then asked why Gabimaru was worried about Iwagakure coming after him even though he is far away from their reach. Gabimaru tells Sagiri that he has no doubt that Iwagakure will come after him because of the name he carries. Sagiri becomes confused by this statement. Gabimaru reveals that his alias, "Gabimaru the Hollow", is a codename meant to carry and pass down Iwagakure's strongest shinobi. A flashback then shows of the Iwagakure chief standing next to the previous Gabimaru after the chief had killed Gabimaru's parents when he was an infant. Yuzuriha explains to Senta the horrific tale of "Gabimaru the Hollow" and how the name alone was feared. Memories then show of the Iwagakure chief telling the potential young candidates on how he will pick from one of them to become the next inheritor. During the training, the chief sets his sights on the young Gabimaru for his impressive skills and his lack of emotions after he watches one of the children throw a rock at him. Later, one of the children is found dead hanging at a tree. The chief asks the previous Gabimaru on the one who committed this act and is assumed that the young Gabimaru is the one responsible. As the killings continued, the chief takes note of how each victim separated the young Gabimaru from the weak. Later, one of the shinobi comes up to Gabimaru after becoming impressed that he carried out a dangerous mission. With admirers and peers that envy him, along with having true talent, the chief decides that Gabimaru will be the next shinobi to inherit the alias. The chief tells Gabimaru that he has chosen him as the next successor and must complete a ceremony where he has to kill the current Gabimaru in a fight. Gabimaru successfully kills the previous carrier and is approached by his admirer in excitement, much to his annoyance. The chief becomes pleased with the results and proudly declares that Gabimaru will become the strongest Gabimaru the Hollow. In the present, Shugen orders the ninja to kill anyone they encounter except the Yamada Asaemon. He then leaves off with Isuzu and Kiyomaru while Jikka decides to sit the rest out. Jikka sees the ninja that admires Gabimaru standing next to him and says that he knows that Iwagakure has their own agenda on the mission. The ninja remembers the chief's orders to kill Gabimaru in order to become the next "Gabimaru the Hollow" and tells Jikka that they share the same goal since their objective is to kill all others. However, the ninja tells themself that the only thing that was more important than killing was to bring "him" back and smiles. They then remembers the time Gabimaru found them after slaughtering the ones that were envious of his success in becoming the next "Gabimaru". Gabimaru then realizes that the one who has been killing the past candidates was them. The ninja admits to this and explains that they have been supporting him all along and confesses their feelings to him.