You don't get a choice because the author is showing that Riko is unable to resist Onori for long. That's why she waits for you to open it instead of just shoving it in. This happens because Onori's entire route is about pressuring Riko into sex, and Riko succumbing. If you don't want to get onori's dick in your face don't go down her route.
I'm not against choices and branching paths, but the game is in active development and the rapey futa is theone with the most content. If you don't want rapey futa content, don't hang out with the rapey futa.
For that matter, if you don't want futa on male content, don't play the game where you're a small, timid femmy boy with a fat butt and bi-curious tendencies.