Mind if I input my 2 cents vs Ciel? Imo Ciel is one of Kohaku/Hisui's harder matchups. (I'm going to assume Kohaku as main for this, longish post ahead.)
Air to air your best chance is j.b unless Ciel is above you, in which case blocking would be the best choice. Up close grab, if you get into a clash fest with j.a you should win, unless Ciel is falling below you, in which case try throwing out jc as she gets a bit farther away. At a distance you should win in the air with your j.b at same height, and j.c if you are above her.
Ground vs Air you have the advantage with 5b, this is one of the best Anti-airs in the game imo. 5b will beat her j.c, j.b and even her cross-up j.b. On wake up vs air though watch out because 5b starts behind you, and may not work in cases.
On the ground you definitely can't match Ciel's speed, however you should be able to outpoke her 2a with your 2b, and her 2c with your 2c. Ciel will try to get clashes with her 2b, which will beat your 2b and 2c at close range unless you cancel them into 5b then into 5c ~ etc, in which case you might beat her 2b and get a free combo. Ciel's dash is very low and will dodge 5b, and they love using 2a when they get close, so 5c is also not recommended as a poke vs her. Stick out 2b when you see her coming if you clash throw out 2c. Sometimes just throwing out 2c on reaction can work, however some good players may shield this on reaction so use it sparingly. Also watch for them tick throws, Ciel players love them. Against them, 2b is your friend. Command roll in general should not be overly used in this match up just because of Ciel's whiff 5c-5c special cancel, and the 236c super. Hisui rush comes in very handy as well. 214b will clash a lot, and 214c hits Ciel during her dash. 214a can work as a shield.
One thing about this match up is that you can't be too defensive, if you lay too many plants or Hisui defensively, a Ciel player will catch on fast and punish you with either a sword, or her 236C super then get a quick aircombo on you afterwards :/. .
After a KD be very careful if Ciel has at least 100% circuit, remember Ciel players love punishing meaties with 236C. I'd recommend plant summon then 2a meaty, then if she blocks then mixup, if she goes for super then shield cancel and earn a whole bunch a free circuit and a combo.
Oh crap I'm stuck in the corner
. Ciel's power of reset can be a pain but don't worry you still have a few tricks up your sleeve. Your 22c has a few(EMPHASIS ON FEW) very nice invul frames which can mess with her Oki and meaties. I wouldn't recommend 5b if she is coming in from the air because her jb is very fast, and she is probably already on top of you by that time. Command roll does come in very handy in this case. If you want to at the end of command roll you can drop 22c if you are scared of a random poke, or you can throw out Hisui 214 b or a for a clash or meat shield. Watch out for her 2c c pressure it can be a real pain. One tactic that I've done several times(although it doesn't always work), is going for double CH with Hisui. Essentially you use Hisui on wake up then one of 4 things happens.
1. Hisui comes out and beats Ciel's move- KD or free combo for you.
2. Hisui clashes or gets hit- opprotunity to escape from corner.
3. Ciel hits you, but Hisui hits her back- it is a double KD, but you get up first so you can get out of that damn corner, watch for 236c as always.
4. Hisui bugs out- it happens, then Ciel gets a CH, combo, reset.
Again this is just something random you can do if you want, it probably isn't your safest bet for sure.
Overall you just have to play rather carefully in this match up, poke a lot, summon when you can, and use Hisui somewhat defensively.