The Masuzoe Family is one of the largest families within the Yomei Alliance, with its home-turf being the district of Onomichi. Its patriarch is Koji Masuzoe, a lieutenant of the Yomei headquarters. The Family has at least one subsidiary: the Hirose Family.
In 2016, Patriarch Masuzoe and some of his thugs approached Hirose Family Captain Tsuyoshi Nagumo about the family's reduced earnings in the latest months. In order to remedy these reduced earnings, Masuzoe tried to force Nagumo to start collecting protection from Snack Kiyomi; a bar owned by Nagumo's friend and romantic interest Kiyomi Kasahara. However, Nagumo refused to extort Kiyomi, so Masuzoe and his goons kidnapped him and took him to the Mount Senkoji Shrine to beat him for his insubordination. Unfortunately for Masuzoe, Kazuma Kiryu witnessed this and confronted the Masuzoe thugs, eventually beating them in a brawl to rescue Nagumo.
A couple days afterwards, Patriarch Masuzoe learned that Yomei Captain Kanji Koshimizu was going to the Hirose Family offices to discipline the family's lieutenant, Takaaki Matsunaga, for getting into a fight with employees of the Iwami Shipbuilding Company. Patriarch Masuzoe decided to accompany Captain Koshimizu in the hopes that Kiryu would attempt to stop the sanctioning, giving him a chance at a rematch with him. Just as Masuzoe expected, Kiryu did attempt to stop Matsunaga's punishment and Masuzoe took advantage of the incident to attack him with a larger group of goons backing him up. Unfortunately for Masuzoe, even with more of his men helping him, he was still unable to defeat Kiryu in a fight.
The following week, when Takumi Someya of the Tojo Clan came to Hiroshima to negotiate a partnership between the Tojo and the Yomei, the Masuzoe Family were assigned to provide security for the meeting at the Senkoji Overlook Hotel. During the meeting, Kiryu and the members of the Hirose Family raided the hotel while wearing masks to rescue Kiyomi, whom they believed had been kidnapped by her ex-husband, Someya. During the attack, Nagumo briefly took off his mask just as Patriarch Masuzoe entered the room, leading to him getting recognized.
Within the a few weeks, Patriarch Masuzoe would be exposed as a Saio Triad infiltrator within the Yomei and he would be subsequently killed by Toru Hirose on orders from Chairman Heizo Iwami to protect the "secret of Onomichi", which Masuzoe knew about. It is unknown if the Masuzoe Family continued operating after the death of their patriarch or if they were dissolved because of it.