Arima, in search of the sword, returned many times to the former hashira of water, his former teacher. His teacher was an old man with gray hair, a very kind voice, but he did not treat demons too strictly, he understood that all these demons were former people. The old man knew that Arima was a half-demon, "you smell like a demon, but you also smell like a human," he said. He was the only one who took Arima as an apprentice, because of this Arima loved the old man, and treated him like his own father. The guy often visited him. And for one thing, he asked, "who is Hiro?" The old man told him many times, but he didn't tell him something, as he thought. It turned out that the old man admired Hiro very much. He was the old man's ideal.

Here again, Arima, coming to the old man, began to listen to what he already knew about Hiro. "Hiro is a swordsman who wasn't in the ranks of the demon slayers, but he killed them too. And how he killed! All he did was exterminate everyone in his path. He is the 1 who was able to master the breath of the Sun! His teacher was Yoriichi, a strong swordsman, who was considered such before Hiro. Hiro, you could say Yoriichi's deputy. Hiro has always had very good lungs and aspirations. I have heard that he has mastered all the breaths, namely: the breath of the Sun, wind, flame, earth, water, lightning and even the breath of the Moon! I do not know what kind of breath it is, but he knows how to use it. And you. You could barely even learn the breath of water, do you hear, Arima. Hiro is right. I understand that, the demon slayer. Hiro was even able to imprison, as I heard, Mudzan! But I couldn't kill him," the old man said. "Where is Hiro now? Arima asked. "I do not know, but I'm probably already dead. He lived a century ago. He also had a wife. Her name was Aida. She was a former pillar of flame. Her last name was Rengoku. Hiro was an orphan, so he took Aida's last name. Hiro's full name is Hiro Rengoku," the old man replied complementing. "One last question. Why couldn't Hiro kill Mudzan?" Arima asked. "I don't know. Ask him if you find him, cough cough cough! The old man replied with a laugh.