chapter 108-109 are the chapters where it's fully shown them having sex, theres also another chapter where it showed that they HAD sex coz theyre naked on the bed but i can't remember the chapter
and for Rail's quest - if you remember, while titan's are driven by prosperity, beastmen by desire, and winged people by freedom, the elves are driven by i think curiosity or knowledge? so they represent that in the notion of "Quests"
Rail's quest is sex, basically he's doing a whole bunch of research and travelling everywhere to gain knowledge on sex - how it works, what it feels like doing it with other races, how is it done with different races, how one race have sex with another race, just basically everything about sex in that world
that’s wild concept sex of all things. What will he do with that quest/knowledge once completed if it ever will be?
Also so Rail has had sex with all races, if that’s what you mean? Based on your “what it feels like” etc. Or just research based than physical?
Masked guy is a titan right? (Mixed) So is that Rail’s first time with a titan, not, or first time in his whole sex research quest?
Also who’s your favorite character?
its been awhile since i've read the introduction for Rail but i think he's had intercourse with other races for his research, so the sex with Dyne isnt the first time hes had sex for his research but im not sure if Dyne is the first titan hes done it with, i cant quite remember
in terms of what he will do with his research once its finished, in one of the chapters it insinuated the elves just keep researching and doing their quests until they die but they record it in books along the way so that the next generation can pick up where they left off and continue the quest (IF it's a quest that takes a long long time) - i'm assuming that there are quest that dont take long to finish, if that is the case then the elves just move on to their next quest - knowing Rail's quest tho, he most likely will die of old age or whatever before he finishes his quest coz theres a lot of factors that go into sex ESPECIALLY if it's two individuals from different races..
but yea all in all, no one really knows what Rail's endgame is for his quest
also theres been an ongoing thing with Dyne in the community where people think he might be falling for Kouichi - i actually commented my thoughts on this so check it out if ya want!
in terms of favourite character, at the moment it's Baro (≧∀≦)

Has the elf dude fucked with the masked dude yet? Checking