Heir to the Family is the 19th substory in Yakuza 0.
Kiryu is approached by a messenger asking him to meet "a member of the Dojima family who isn't his enemy" at the Yoshida Batting Center. When Kiryu arrives, he is greeted by Daigo Dojima, who admits to sending the messenger. Daigo asks Kiryu to spend time with him, dismissing three teenagers who had been keeping him company, and explains that his father is too busy to spend time with him anymore.
He is aware of Kiryu's expulsion from the family but assures Kiryu that no one will dare touch him while Daigo is with him.
It is implied that the two are quite well acquainted prior to the events of Yakuza 0, calling each other friends, and making reference to Kiryu "playing with him all the time" when he was younger, and insisting Kiryu use a more casual form of address after he refers to him as "master Daigo". Kiryu mentions that Daigo has "always been a good kid", despite his father.
Daigo asks Kiryu to bring him various places around town, such as the arcade and a karaoke lounge that doesn't normally allow children. When the lounge tries to refuse Daigo entry, he states the name of his father to intimidate the bartender into allowing him to stay. Kiryu orders Daigo a non-alcoholic drink and apologizes multiple times for the way Daigo acts while at the lounge; Daigo makes several unreasonable requests, and insults the bartender, the lounge itself, and the hostess who sits with him. Kiryu chastises Daigo for his behavior, stating that it's unlike him to be so rude to a woman. Daigo blames his bad mood on not having any real friends, due to his position as the patriarch's son.
On the way out of the lounge, Daigo is cornered and kidnapped by three masked men. After tracking them down and beating them in a fight, Kiryu unmasks the group to reveal they're the same three teenagers that Daigo ditched at the beginning of the substory. Daigo wants to punish them in return for the beating they gave him, but Kiryu scolds Daigo for acting like a spoiled child, and that he should know better. Daigo breaks down and apologizes, explaining no one disciplines him due to their fear of his father. Kiryu advises him that he can't just rely on his family name and wealth if he wants to have friends and peers treat him as an equal.
Kiryu offers to escort him home, but Daigo states he'll be fine on his own. He asks once more for Kiryu to be less formal with him, and addresses Kiryu more respectfully (calling him Kiryu-san rather than Kiryu-kun) before taking his leave.