All For One/Relationships

All For One's Brother
In the past, All For One cared deeply for his younger brother as he was the only family he had. However, All For One did insult him labeling him as pathetic and fragile as he had his bodyguard go easy on him before imprisoning him. In return, All For One's brother had a strong sense of justice and did not back down from opposing his brother's evil deeds. To end his rebellion, All For One attempted to get him to submit by giving him a quirk unaware that his brother already had one and his act only formed the creation of One For All. All For One's younger brother attempted to defeat him with his newly merged Quirk (now called One For All), but didn't have the sufficient power to do so.

It is unknown if All For One killed his brother in battle but the latter's quirk was passed down to an unknown successor, in the hopes that someone in the future would eventually stop his evil older brother once and for all.

Tomura Shigaraki
All For One is grooming Tomura as his successor. He was the one who rescued Tomura from being alone after the incident of killing his family during his childhood. All For One is deeply invested in Tomura's growth and was pleased when Tomura finally developed a plan to achieve a goal on his own. When the police and Pro Heroes capture Tomura, All For One retaliates with force before teleporting Tomura and his friends to safety.

It is unknown whether Tomura is aware or cares that All For One killed his grandmother, however, it does appear that All For One truly cares for Tomura, having a similar relationship like All Might has with Izuku Midoriya. Instead of punishing Tomura like any archetypal villain would do to their apprentice, All For One instead encourages Tomura to simply start over as many times as he needed to and that he will always provide him with help.

Kurogiri
Not much is seen between them, though Kurogiri seems to be loyal to All For One. All For One entrusts him into looking after Tomura and ensure that he is given the proper guidance.

All Might
All For One detests All Might. He hates the One For All successor for incapacitating him, defeating his comrades, denying his ambitions and being called the symbol of peace for this.

He states to All Might that he needed a successor because of the injuries All Might inflicted on him from their first battle. Due to the crippling injuries All For One received he can never be in his prime again. It's also heavily implied that All For One is in an even worse shape than All Might is. While All Might's injuries limited his use of One For All, All For One is not capable of living without a life support apparatus keeping him going.

During their second battle at Kamino Ward All For One confesses that he still has nightmares and mental trauma from their first encounter from when he saw the look on All Might's face after ripping All Might's guts out. All Might seems to not only be the first to defeat All For One, but also the first to ever severely scar him mentally.

All For One enjoys belittling and ridiculing All Might, even relishing in breaking All Might's spirit by revealing that Tomura is Nana Shimura's grandson. He also enjoys watching All Might become riled up by belittling Nana's heroism and death. In their second battle, All For One aims to take everything from All Might, his image and pride by revealing his gaunt form and weakness to the public.

Even after being captured, All For One continues to play with and taunt All Might, using any and every opportunity to strike at his nemesis. Despite being defeated by the latter, All For One took his loss in stride and mocked All Might for not dying when he had the chance, confident that his pupil will become stronger to take over the League of Villains. All For One is also aware of the fact that Izuku Midoriya is the current bearer of One For All and criticizes All Might for being a pathetic teacher.

Nana Shimura
All For One thinks Nana was a pitiful woman. He mocks her commitment to ideals and disparages her strength and, by his admission, declared the latter died a pitiful death.

All For One tarnished her memory by knowingly taking in and grooming her grandson to be his successor.