Minor correction: Ultima Regio means 'final king', so if the Japanese text says 'last army', the furigana is probably meant to be read as Ultima Legio.
It's skipped in the manga, but in the novels, they fucked when they were at Erika's house.
Erika acts very sensually in front of Touka to see what kind of man he is and he doesn't react.
Seras asked him if he's not interested in sex and he explains that his parents often had loud sex in the room next to where he was, like if he didn't exist. That's why Touka associates sex as something disgusting.
Seras asks him if he wants to change this impression with her and he agrees. The next day, Erika told them that they look like their relationship has moved forward.
It's skipped in the manga, but in the novels, they fucked when they were at Erika's house.
Erika acts very sensually in front of Touka to see what kind of man he is and he doesn't react.
Seras asked him if he's not interested in sex and he explains that his parents often had loud sex in the room next to where he was, like if he didn't exist. That's why Touka associates sex as something disgusting.
Seras asks him if he wants to change this impression with her and he agrees. The next day, Erika told them that they look like their relationship has moved forward.
I do believe the "Ultimus Regio" is not "the last army", but rather a reference to "Ultima Ratio Regum" - "last argument of kings", which generally is a reference to the use of force (like declaring or waging war). It's the motto of many an artillery regiment of the world, so it can be taken to mean just "hard hitters".