|Side||Against the Hero Association but has nothing against the public.|
|Family||Tongo Mizushima [Son -deceased]|
Mrs. Mizushima [Daughter-in-law -deceased]
Crea Mizushima (granddaughter)
Mirea Mizushima (granddaughter)
|Power(s)||Genius I.Q. with considerable knowledge in advanced technology and bio-genetics|
|Occupation||Former R & D scientist for the S Project|
Second-in-command of Jackal
Append Gear Maintenance
Ratman's Technical Support
The Birth of Smallest Hero
Gengo Mizushima is second in command of Jackal. He is the grandfather of Crea Mizushima and Mirea Mizushima. Since he has the same last name as Tongo Mizushima and is Japanese, that would make him Tongo's father while Tongo's wife (an Englishwoman), was his daughter-in-law.
Gengo is a short man, even shorter than Shuto, with an almost completely bald head. He always wears a white lab coat and carries around a clipboard.
Despite being elderly, he is very active in the day to day operations of Jackal. He also greatly cares for his granddaughters from taking them in after their parents died to praising Crea on her "diabolical plans". He also exemplifies the stereotype of the "mad scientist" as he sometimes uses Shuto as a literal lab rat for his side-experiments, (such as an experimental growth serum, which actually turned Shuto into a child for a while). Like Crea, Gengo wishes for Mirea to have a normal life.
He used to work alongside Dr. Teramishi and the parents of his granddaughters Crea and Mirea. He was brought on to help work on the S Project that created Shiningman in order to bring hope into the world. He left the project and has been raising his granddaughters ever since their parents died. He, together with Crea, started Jackal and created the Ratman suit.
First Crimes Arc
Gengo is with his granddaughter Crea Mizushima, when they try and succeed to trick Shuto Katsuragi into signing the contract to become a member of Jackal. The next day, he thanks Shuto for his work yesterday and also asks how his body feels. Later after Shuto's first assignment is done, he analyzes the data that Shuto had brought back. A day later, Gengo helps with Shuto's training within the virtial reality world. After the training, when Shuto complains about the training, Gengo informs him that Heroes will attack him in numbers. Another day later, Gengo is with the other of Jackal as the have a hot pot. He listens as the other talk about what Shuto did yesterday.
Hero Awards Arc
Later during the Hero Awards, Gengo along with Crea notices that Shuto vitals are rising when Shuto turns into Ratman. Later, Gengo fixes the append gear when a malfunction happens.
Threat of S Arc
Days later when Shuto heads out to help Mirea from being linked to Jackal, Gengo moniters Shuto vitals. Gengo then notices a spike and begins to worry about Shuto. Gengo then helps Shuto recover, when Shuto gets back.
Normal Life Arc
A few days later, Gengo talks with Crea about how she doesn't have to carry the burden along, as she has all of them.
Another day later, Gengo is with the others and listens as Shuto talks about when they ran into an android and its creator.
Hero Booster Arc
Days later when the heroes go berserk and Jackal manages to capture one, Gengo finds a smartphone on the berserk hero that the Jacky Combatants had captured, and discovers that the device is transmitting the power of the S Gene. Using the same idea, he aids his granddaughter in transmitting the antidote to the Hero Booster Program.
Gengo is a top-notch scientific genius, with expertise in advanced technology and biological experimentation. Currently his position is to maintain and upgrade Shuto's Append Gear. He also performs side-experiments, such as making an experimental growth formula. Since he was part of the S Project, it is very likely he knows about the secrets of the S Gene and Shiningman's powers.
Gengo dearly loves his granddaughters and will do whatever it takes to help them, even if it means going against the Hero Association.
Basically he considers Shuto like a lab rat for the Ratman Suit and the Append Gear, though he does show concern over his health and how his powers are evolving. He also confirms that Shuto has the S Gene with the statement that 'only that kid can be Ratman.' He does seem to care for him however, as the formula he makes was supposed to make him taller, something Shuto has expressed a desire to be for quite sometime.
He reveals in a casual conversation that he knew of a colleague of his that adopted a boy that supposedly had supernatural abilities. This was revealed to be Dr. Teramishi, whose immoral side-experiments in bio-weapons for profit, got him fired from the original Shiningman Project by Crea's father. Gengo holds no respect for his former colleague, and thinks of him as an opportunistic and immoral character. He was just as horrified as Crea when Teramishi blamed Jackal for the Hero Killers.
It has been hinted that Rio's father was Tongo Mizushima's friend, and therefore Gengo was also close to the future president of the Hero Association. After his son and daughter-in-law's deaths, it is very likely that Gengo also held a grudge towards Shouichirou for his involvement in that incident.