I mean, at face value, one could say that Eiji is holding Ash back and causing him to act, or not act, depending on his presence or the situation. That being said, Eiji is not used to the environment that Ash has grown up in, yet he is willing to immerse himself in it to try and help him, in his own way, because he cares about him. When you care about someone the way that they care for each other, logic doesn't always dictate the situation, especially when put in dangerous and adrenaline-inducing circumstances. One could argue those are reasons Eiji should've removed himself from Ash's life, and went back to Japan, but Eiji knew what he was getting himself into. Though, that isn't what most people were concerned about. It was more so that Ash was willing to put his life on the line for Eiji, and Eiji was physically weak and not mentally capable of killing someone. If Eiji was so capable of just picking up guns and shooting people, they wouldn't have had the relationship they did in the first place anyhow, because Eiji wouldn't be what makes him Eiji.
Eiji's existence made Ash feel his life had some semblance of normalcy and warmth, amidst his life of violence and trauma. Before he met Eiji, there wasn't much purpose to his life other than violence. Eiji made his life about more than that. If Ash really wanted Eiji gone, he could've done something about it, but he didn't, and he knew the risk he was posing to himself in not doing so. (By gone, I just mean having him toted back to Japan, or something. Lol.)

So I saw the anime and read the manga and I really liked it so I showed it to a friend of mine. She seemed to like it, but as the episodes went on she just didn't like Eiji anymore. It wasn't to the point of hating him, but I was just shocked that she just didn't like him. I guess it was because Ash went through all this trouble because of him and things would also get more complicated when he was involved. She just couldn't understand what was so great and special about Eiji even though different characters including Ash would say what made Eiji so special throughout the anime. I thought it was made clear why Ash needed Eiji in his life and would do anything to keep him safe.
So I'm just wondering if there are others that think the same way as my friend does or think differently.