Daiyousei doesn't appear to have any skills saying she's sensitive, but for some reason she's only just started getting fucked and yet she cums way faster than Meiling or Sakuya did. Meiling does it a lot now, but this is like two seasons of tormenting her in bed. I first had sex with the fairy like 4 days ago, and she's already at a point like we've been doing it for a few weeks.
Do some girls have hidden stats that make them cum faster?
Rather than Daiyousei being easy to make cum, Sakuya and Meiling are difficult due to traits. Sakuya is Vaginal Insensitive and Self Control hurts sexual gains. Meiling also has Self Control and Reserved, making her even more difficult. You can mouseover those personality traits to get info on them.
Daiyousei does have a ton of traits that makes her more docile and easier to push down (Timid, Docile, Calm, Curious), she's one of the most submissive characters in the game. Though she doesn't have much to increase the ease of making her orgasm directly, she is easier to build into an orgasm machine since she's so submissive and will go along with your training so quickly/easily. Only thing that really hurts her is Misandrist which can penalize you before she's at "Love".
On the "Ease to train/make orgasm a shit ton", I think Daiyousei is like a 2-3/10 difficulty, Sakuya is probably around a 6/10, Meiling is like 7/10. Sakuya is the hardest to judge because she has a lot of conflicting traits. She's super resistant to sexual commands but she also has some stuff to increase her enjoyment once she finally agrees to stuff.
It's pretty nice how much variety the traits allow. So many factors in training a girl that are checked. Ease to push down for sex, ease to agree to various sex acts, ease to enjoy pleasure, ease to gain sexual exp, sensitivities, ease to agree to raw penetration, etc, etc. I haven't found any girls yet that are easy or difficult in all regards, they all have a strength or weakness or two.
Edit: Wait, scratch that. I found the game's largest slut. Apparently I picked my TSP cumdump well in my first run. Every single one of her traits makes her easier to lewd/train. I guess she's going to be my vigor dump in my newgame+ too, lol.