for the 3te battle try at the start to buff up 空帯雷の術 3times than 気功泉の術 3 times than 空帯雷の術 than 気功泉の術 (this way you should have both buff's max with the longes possible turn time). after spending 8 turns for buffing up you should hit her with 攻撃. your buffs should both run for around 10 rounds full atk buffed you make around 50dmg+ with 100% hit because of that she hit's her max ecstasy every hit you make and starts useing her turn for mastrubating. also befor your buff's run out use the HP skill 天女衣の術. if your HP is under 150. your SP should get fully filled up in the time you hit her. the 観察 skill is only usefull if your ecstasy is over 40 at 60 you should use it with the def buff 金剛鱗の術. repeating the buffing and hitting whil holding your HP high with the 天女衣の術 if needed should easily get you 60 turns+. you should also save all 3-5 turns because when she uses her spezial handjob skill you load the save thats 3 turns back and repeat since she uses them sometimes randome. the rest is luck at somepoint she is going to use a new spezial skill wher you get a choice. (at this point it's scripted that your going to lose) 1. lets to the new one 2. to the handjob skill after that to the new one if you survive it. advancing from the first choice you made you come to 2-3 more choice's or die. if you made all right choice you see the ending.
it's just to bad and boring that you can't win but hope that helps you to get a A or S ranking.