do you think about riku and towa's relationship
Do I think about it? Not really.
I know some people are against it based on the age gap, but in the grander scale of anime relationships, I think that—so far—it's one of the less problematic ones.
I don't particularly care about age gaps in anime relationships. Going off of Yashahime canon, there's not that much of a difference in age between Towa and Riku vs. Kagome and InuYasha. They're both clearly coded as teenagers, so...whatever. Ship what you ship.
(The SessRin problem lies in the fact he knew her as a literal child, raised her, cared for her, etc; not in their age gap. It's grooming. If Rin had been "close" to Sesshomaru's age originally—both of them being drawn as late teens/young adults—then there wouldn't have been an issue. Their whole dynamic would've been different. But that's not the story that was told.)
Now Kirinmaru and Towa—I'm definitely not here for that one. They're clearly coded (or drawn or whatever) as a child/teen and an adult, respectively, and behave accordingly. A relationship between them would be pedophilic.