Drain/Sacrifice are percentage-based attacks so they do a ton of damage to any enemy regardless of their defenses and restores HP to the caster which makes it almost impossible for Yeeua/Angel to die if they're spamming it and can't be one-shotted. Drain appears to be Shadow-element and Sacrifice is Light-element, however, so in general (Greater) (Mass) Sacrifice will do 60%(!) damage to things more frequently, as more things are weak to Light than to Shadow. (Greater) (Mass) Drain is better against those church guys though. The best spot to grind experience is probably B3F of the tomb dungeon because everything there is weak to Light so you can have everyone but Angel Defend and just spam Mass Sacrifice and then Greater Mass Sacrifice, which will win any fight in two turns. Seems to give more experience than B4F where skeletons aren't weak to Light (for some reason they're weak to Fire instead).
Yeeua's Petrify attacks seem possibly broken, too. They are listed as a 50% success chance like all the other status effects but I haven't ever seen them actually fail. A petrified enemy is unable to act but petrification doesn't break when they take damage like Sleep, so once she knows Greater Mass Petrify it seems like you wouldn't be able to ever lose any fight because she could just spam it every turn using MP recovery gear and the enemy would never act. Neya kind of sucks in comparison but I think she gets Greater Mass Inspire Courage which appears to double the entire party's stats, so that's probably really good if you just use her as a healer and buffer.
Also, if you don't use ki you will fall behind the enemies statistically and be unable to damage them with physicals. The stats seem to be pretty binary in the sense that if you don't have enough Attack to overcome Defense you just do no damage (and the same applies to you for enemies). Investing ki primarily in Attack, Defense, and Magic Defense, and farming it from h-scenes, will make the main characters vastly stronger. Note that Jeanne and Leanna can't use the Ki Orb until Jiao has had sex with them once (seriously, that's how you unlock that). Jiao/Jeanne/Leanna seem to be best built as physical attackers because they can each get 3 or more attacks per turn from h-titles, which triples or better their ki investment in Attack and massively increases their TP gains. Jeanne kind of has bad TP skills for attacking though but she can still do a bunch of regular attacks and then use her TP for buffing or something. Jiao flattens everything with 50 TP and Leanna has a number of single-target attacks, AoE, and buffs that are pretty cheap so she can probably alternate between that and attacking to recover TP.
Xiong is ironically really bad at physical attacking because he doesn't seem to have access to multiple attacks so he can't farm TP or do a lot of damage except by using the skill that drops his defenses. However, his titles give him up to a 30% boost to all of his stats at once so he's probably a really good mage because he could dump a ton of ki into Magic Attack and HP/MP/Defense and be a tanky caster with infinite MP. Spells seem to do a lot of damage even with low stats (the familiars seem to do decent damage when hitting weaknesses, anyway, and they can't use ki) so I presume if you stat dumped his Magic Attack and equipped his best title he'd just instantly kill everything with AoE magic. The only real use for his TP seems to be in lowering enemy Defense, which would let the girls murder bosses and such in one turn to get around the insane regen a lot of things have. Haven't actually put this into practice but I suspect he's probably low-key OP, it just takes way less work and effort to get Jiao to the point where she can kill anything with one TP move.
Yeeua's Petrify attacks seem possibly broken, too. They are listed as a 50% success chance like all the other status effects but I haven't ever seen them actually fail. A petrified enemy is unable to act but petrification doesn't break when they take damage like Sleep, so once she knows Greater Mass Petrify it seems like you wouldn't be able to ever lose any fight because she could just spam it every turn using MP recovery gear and the enemy would never act. Neya kind of sucks in comparison but I think she gets Greater Mass Inspire Courage which appears to double the entire party's stats, so that's probably really good if you just use her as a healer and buffer.
Also, if you don't use ki you will fall behind the enemies statistically and be unable to damage them with physicals. The stats seem to be pretty binary in the sense that if you don't have enough Attack to overcome Defense you just do no damage (and the same applies to you for enemies). Investing ki primarily in Attack, Defense, and Magic Defense, and farming it from h-scenes, will make the main characters vastly stronger. Note that Jeanne and Leanna can't use the Ki Orb until Jiao has had sex with them once (seriously, that's how you unlock that). Jiao/Jeanne/Leanna seem to be best built as physical attackers because they can each get 3 or more attacks per turn from h-titles, which triples or better their ki investment in Attack and massively increases their TP gains. Jeanne kind of has bad TP skills for attacking though but she can still do a bunch of regular attacks and then use her TP for buffing or something. Jiao flattens everything with 50 TP and Leanna has a number of single-target attacks, AoE, and buffs that are pretty cheap so she can probably alternate between that and attacking to recover TP.
Xiong is ironically really bad at physical attacking because he doesn't seem to have access to multiple attacks so he can't farm TP or do a lot of damage except by using the skill that drops his defenses. However, his titles give him up to a 30% boost to all of his stats at once so he's probably a really good mage because he could dump a ton of ki into Magic Attack and HP/MP/Defense and be a tanky caster with infinite MP. Spells seem to do a lot of damage even with low stats (the familiars seem to do decent damage when hitting weaknesses, anyway, and they can't use ki) so I presume if you stat dumped his Magic Attack and equipped his best title he'd just instantly kill everything with AoE magic. The only real use for his TP seems to be in lowering enemy Defense, which would let the girls murder bosses and such in one turn to get around the insane regen a lot of things have. Haven't actually put this into practice but I suspect he's probably low-key OP, it just takes way less work and effort to get Jiao to the point where she can kill anything with one TP move.