I think Riou is a really tragic guy because his whole character is based on his desire to be of use to others. Even with the military, as much as I like his dynamic with his comrades and Kubiki, he's also seen as someone to be used as an asset rather than a person to be protected as well. It must've been torture how how his desire to be useful lead him to going MIA and staying isolated in the woods. He never had a friend that didn't evolve away from that "i need to assist them" dynamic until MTC. It must've been jarring for him.

Thats why i think the "do I look like a piece of shit to you" dialogue is so important to me. Riou just downplayed his need for help to Samatoki, saying that he doesn't need to help as it's his burden to bare, and Samatoki immediately shuts that down. His insistence that friends help each other out and that it would be a dick move to always take from Riou and never help in return was definitely a core moment, especially the reprise. "Tell me, Samatoki. Do I look like a piece of shit to you?" makes me crazy.

Thinking about him and MTC's dynamic only makes me sad about his past pre DRB but I'm glad it's gone away from him being alone by himself. I do wish we get backstory soon though...sighhh