There have been some comparisons drawn between Denji and Arajin, but I feel like these lack an understanding of what really sets them apart. Denji wants to "lose his virginity" because he has nothing, Arajin wants to "lose his virginity" because he has everything.
Part 1 Denji is deprived, surviving day to day in fear of losing his basic living conditions. The few stabilizing emotional connections he is able to make are offset by the presence of manipulation, grooming, and abuse. Arajin has everything a growing teenager should be provided: food, shelter, the love and support of his guardian, the space to practice both his hobbies (seal carving, music) and life skills (cooking). The one thing he lacks is a relationship with a peer (both in regards to friendship and romance). Having had all his basic needs met, it would make sense for him to want to pursue this type of emotional satisfaction. So when presented with the opportunity to wish for literally anything, he chooses the possibility of intimacy with another person. Arajin is a generally happy (though perhaps insecure) teenager and his mundane life satisfies him, leaving him with simple desires. Denji, in comparison, is desperate for the stability of having his basic needs met and even when they are, they come at the cost of him having to do work that causes him great physical and emotional harm. The banal desire of "losing his virginity" thus takes on different implications, being framed as a reward within his means, something achievable that will give his life and suffering meaning. It's horrific.
In comparing these characters' motivations and situations, I am not trying to push sympathy towards them one way or the other. Rather, by understanding the roots of these characters' desires, we can better understand their roles in their own individual stories. Arajin's seemingly petty desires are meant to contrast with Matakara's. They both essentially want the same thing (an intimate relationship with a peer), but Matakara's more precarious home situation makes him emotionally unstable in a way that twists his desires, setting him on a path towards violence. Despite Arajin's lackluster personality, he is ultimately more equipped to handle his own emotions as a result of his upbringing, which is a point the story is trying to make: that all children should be given the opportunity to grow up without lacking in their physical and emotional needs. In a way, this applies to Denji as well. A world that loved and provided for Denji might still not have made him the most good or likeable person, but it would have hurt him far less, and that in and of itself has value.
