Part of the charm of Dead Souls is the ability to run into the Quarantine zone for free time. You can run around slay zombies, collect items and experience, but you don't have to do it alone! There are a variety of partners for each guy. One of Ryuji's partners is a host, by the name of Junya. Before Junya will join Ryuji in the zombie slaying, Ryuji has to collect three different items so that the host will be "prepared." Begrudgingly (both the player and Ryuji) collect the items and drag the squirming, crying, pretty boy into the Zombie infested parts of Kamurocho to save his friend.
Initially, Ryuji doesn't care what happens to Junya. He buys the gun from Kamiyama so that Ryuji can continue to use the shop. When Ryuji leaves he runs into Junya again and the host seems to think that Ryuji should help him. Ryuji declines until Gary steps in and tells him to collect the items that the host wanted. Ryuji fails to see why he has to "bust his ass to help out." Ryuji does it anyways and ends up being a mentor.
Junya
At first, Junya has absolutely no confidence. He attaches himself to Ryuji almost instantly knowing that the other man is strong and capable. Ryuji reluctantly agrees to assist Junya in finding his friend. Through the course of four substories, Junya slowly gains confidence thanks to Ryuji's gentle prodding. I use gentle in a loose fashion that generally involves Ryuji telling him to man up, be a man, or to just shut up and do what he needs too. If he has the resolve to save his friend, he needs to stick to it. Ryuji is short with him but not necessarily mean.
Eventually, when Junya finds his friend he's knocked out. Junya whines about how hard he worked to save his friend and now he can't even show off. Ryuji tells him that he'll have to deal with it as they make their way out of Quarantine. With Ryuji's help, Junya saves his friend. It's a happy little story about Ryuji being a mentor and helping someone save their friend.
I think its funny because Junya spends so much time trying to be "manly" and "cool" that he doesn't realize he looks like a fool. Ryuji ignores his antics except for when he is correcting Junya's low self-esteem. Ryuji has a bit of "You're a man, act like it" attitude, but when Junya desperately needs help, Ryuji is right there to assist him. I believe that he was the same with his boys, as the boss of the Go-Ryu we know he put up with very little (especially if it annoyed him) but when his boys needed him, they knew they could rely on them. I don't think that Junya is anywhere close to being accepted into the Yakuza. Thankfully, Ryuji retired (forcibly but still) from that life.