Maaaan, just... wow.
Of all the routes, Ryou chose the revenge one.
Reiji got legit fucking pissed after hearing Nagi's backstory and now wants to take everything back at Mao. A rage enough to awaken his dormant dick. It seems the erectile dysfunction was due to Reiji's lack of a reason to live. Still, killing Mao is what Nagi wants??
And here we were shown why mother = son... or maybe, the child surpassed her (single) parent. Reiji used sex to domesticate Yuri and have her under his thumbs, with a clear threat if she disobeys his orders. Something, IIRC, Yuko has never done to her "hitmen", Uryu and Gen. It's obvious he hates his teacher, but for the time being, she is useful for a facade. And Yuri went from happy to scaredshit after doing the deed and hearing Reiji's orders. It's like she picked the real reason why he is happy to be alive, and she doesn't like it.
Maybe this is how Yuri will realize Reiji isn't worth to spend her life with and may free herself from her abyss after realizing no matter if it's a double suicide or a solo auicide or risking getting death penalty'd for killing someone. Reiji is set to die with Nagi and won't hold himself back. Reiji is gonna ruin his life by tainting his hands with blood, even if the reason is hauntingly selfless in the bad sense (take the rage Nagi can't feel towards her uncle as his). In the end, we are heading a straight path into a lovers suicide end.
I hope you have found out the hidden Attack on Titan reference here. Reiji going to kill Mao is literally Eren's rumbling in the main concept: MC taking the repressed emotions another person can't feel, make them his and go on a murderous spree.