First off, I gotta say the interactive sex scene with Khenbish + Tuan was impressively written and basically everything I could have hoped for, so kudos on that!
Here are my thoughts + ideas for Asterion:
1. Vanila stuff is fine, and I think oral for Asterion, oral for MC. 69ing, and frot would be the main things I'd love to see. Maybe stradding his muscled chest while both nude. Maybe something where the MC gets Asterion to go on all fours, before ducking under him and 'milking' him ;)
2. Tail tugging, tail licking/nibbling or gentle crotch groping. Slapping on the ass. Biting/licking pecs + nipples.
3. Hmm, probably put his bovine tongue to use in some teasing fashion.
4. Some random ideas: Pool scene unlock: (Asterion or MC loses their swimming clothes while swimming, or MC/Asterion gets frisky and dives underwater to do naughty things to the other)
Gym scene unlock: (Asterion tries to bench press a hefty amount, MC has some kinky fun with his lower half.)
Shower scene unlock: (After a particularly messy R+D project MC and/or Asterion get covered in dirt or mud and go to wash off, before being joined by the other as a surprise.)
Restaurant/Bar scene unlock: (New fancy booths/tables - maybe with tablecloths - lead to MC/Asterion having a dinner date that leads to either one 'dropping a utensil' and ending up between the legs of the other - cleverly concealed but still in public.)
Office/work scene unlock: (Similar to the above scene, but instead its when MC or Asterion is busily working at a desk and the other 'interrupts them' and hides under the desk while other employees come and go.)
5. Probably something like the public sex scene above is as risqué as I would get.
6. Not sure!
7. Asterion taking charge, showing initiative or being surprisingly sexually aggressive - but still gentle.
8. Worshipping the MC sexually, putting MC's pleasure above his own much to MC's annoyance. Perhaps having his tail played with during sex being a guilty pleasure of his.