How to deal with *enemy spoilers*?

[Purazis]

Yukkuri:
I managed to kill the 1st time, but afterwards she always flee before I can kill her. I'm not sure if I got lucky or if you can abuse her script by using spells, not attacking with all characters or something like that. Otherwise your exploration team needs Aya + multi-hit attackers. It pains me so much seeing that juicy XP taunting me as it runs away.
Tewi
Beat her by brute-forcing with Alice's Parar and lucky dice rolls, but I'm curious on how to deal with her Ancient Duper. Reimu's Dispel didn't work on her. The description is confusing, with the short version telling it dispels only negative Variations, while the extended description saying it removes all debuffs. There's also the augmentation that improves so it only removes debuffs, which I didn't have it. Tried Silence (with Mokou 2x infliction chance), Poison and Blind Permanents with 5X Infliction (Tewi has 45) but didn't manage to debuff her once. Maybe Confusion or Topple? Also none of my characters had Spell Interrupt by the time I went to face her. Didn't bother with Satori blue magic yet, too annoying without Control. Maybe the idea is to just tank it away with Light Defense accessories with 2 or 3 characters?

[HakanaiBlue]

At the point you're at, I think your best bet for dealing with yukkuri by securing the first turn with Aya and using physical attacks. Multi-hit moves like Sakuya's are good, and Youmu also has a move called Yukkuri Slash that deals extra damage to them. Extra accuracy helps, but they have a stat called Emergency Evade that gives a flat dodge chance independent of their evasion. You'll know that they dodged with Emergency Evade when the miss text shows up in green.

Sakuya's Private Square is also very helpful in getting a couple extra turns to do damage, even if it means she'll be the only one attacking.

As for Tewi, her accuracy stat is low to begin with, and Ancient Duper is even less accurate on top of that. You can lower her accuracy further by applying a debuff like Satori's Hallucinatory Arts. If her accuracy buff is on, this will cancel it out. Reimu's Dispel Talisman (which should say just "Var" instead of "Bad Var," will ensure this gets fixed, sorry!) as well as the Dispel Staff skill (available from the staff augmentation tree) can also remove her accuracy buff if you'd rather go that route.

Sanae's Wind of Foresight is probably a good idea to keep on for the entire fight as well. I think a couple other characters have helpful options for evasion too, so this isn't an exhaustive list by any means.

[Aria Kawa]

You've said pretty much everything about yukkuris already. In my case, I used the sonic stream formation for most of the game since it gives you preemptive which makes the battles way more easier and it also helps with yukkuris. I don't remember how I've defeated that boss, but I probably used Alice too and Satori to debuff varieties instead of permanents.

The boss of the following stage is a duo battle, you either burst the two before they make too much damage, or try to inflict one of them with control permanents like berserk or charm.

[Purazis]

Thanks for the answers.

[radotyre/j2]

seconding the private square advice. Make Aya commander and use her bomb so she can cast it before they can escape. Plus you can actually hit the damn things since private square turns off evasion.
The downside is that Sakuya and Aya might become overleveled compared to others