Kei Senju

Kei's first memory is falling off a swing and breaking his leg. He remembers seeing parents of other children look at him and nobody going to him to help. His second memory is being in the Hokage office, receiving the news of his ‘parents’ dying. He doesn't even know who they are. He is later thrown into an orphanage. He joins the Academy being almost 1 year younger than everyone else. He doesn't care about making friends or such novelties. He just wants to graduate.

After the Chunnin exams, he meets his Aunt Tsunade for the first time. Her first words to him are ‘You look exactly like Uncle Tobirama’. For the first time in 12 years he believes he found his real family. It takes him by huge surprise when he realises Tsunade has absolutely zero interest in him. The only reason she agrees to train him alongside Sakura is because he doesn't leave her alone until she does.

Before the Pein arc, Kei trains a lot with Neji and Lee, and learns a few Ninjutsus. It is then when Tsunade offers him a scroll passed down from generation to generation in the Senju Clan and he learns so many things that his Grand Grandfather created. During the war, when he sees Senju Tobirama, he almost starts crying. Tobirama ends up patting his head although he is shorter than Kei. He finally ends up letting go of the resentment he had for the Senju clan after the war.

Post-War / The Last / Boruto

After the war, he decides to stop working as a Shinobi and focus solely on the hospital. He is still in contact with Aya and Ran, although he barely has time to see them. Every time they end up in the hospital he doesn't discharge them until he finishes his normal nagging session.