Miyama Gaku

Miyama Gaku (深山 萼) is the president of the Miyama, 5th generation subgroup directly under Tokusa, the largest Yakuza group in the Kanto Region. He shared a sake and sworn ties with the Miyama Group 5th generation leader Somei Renji to end the 60 long years of feud between two factions.

Appearance
Gaku has a white haircut and has a scar near his left eyebrow since he was younger. When he was younger, he technically looks a lot like his great nephew according to Somei Yoshino when Kirishima pulled his hair back.

Personality
It is unknown much about Gaku, other than he is not actually married or have any children. Kirishima is actually not his grandson, but rather his great-nephew. He and Renji are friends and when they were younger, he used to tease Renji with the name 'Renko-Chan'. He, like many characters of the series has a smoking habit.

In one of the sketches/extra of the series, he is revealed to be the black sheep of his family and they no longer talk. He is also a bad caretaker, as he only hands Kirishima some money and does not care for him further than that, therefore allowing Kirishima to grow up independently without family love. He can also be rather heartless, as he lets Kirishima's abilities decides for his fate, and doesn't seem to care if he dies.

It is revealed by Renji that Gaku can fight very well and how Renji could never beat his level. He is also mentioned to be extremely gifted at games like rock paper scissors.

Somei Renji
Renji and Gaku are friends since they were younger, and they both worked together to end the feud of the Miyama and Somei groups, as well as sending their grandchildren to forced marriage. Renji also knows that Gaku cannot bear with alcohol, and will feel sleepy. There is a point that Renji was driving Gaku's car and felt off a cliff, and Gaku laughed it off before beating Renji up after Renji told him about his car. Renji also mentions that Gaku is extremely good and skilled in combat, and how he can never beat his level.

Miyama Kirishima
Although Kirishima refers to him as a grandfather, biologically he is the latter's great uncle. Gaku never really cares for him, and only gives him an amount of money for him to save up from eating. He also hit him once for actually calling him 'Gramps'. Despite not really being that good of a grandparent, he is always having his eye for him, and is disappointed when he found out that Kirishima has fought the gang members of Akaza Shiori.

Somei Yoshino
Although they have not had many interactions, Yoshino's first impression of Gaku was that he looked really cool.

Trivia

 * Miyama Gaku actually is not married nor have any children, therefore he seems to never know what is it actually like to raise a child like Kirishima.
 * Gaku cannot drink sake, and feel extremely sleepy once he takes a sip.
 * It is shown that Gaku earned his scar since young, but for a reason that is unknown.