I'm not sure if there's a lot of overlap between PADfags and 2HUfags for the few of us here to give plausible feedback, but I guess I can try.
>Rumia
AS: Replace light orbs with what? Dark orbs? The CD is 1 turn too fast if that's the case.
LS: Gimmicky, but plausible, I'd say.
Awakenings: Not much to comment on.
>Cirno
AS: Seems okay to me.
LS: 3.5x for 9 orbs feels a bit lacking for what I assume is originally a 5 star. I know the ⑨ meme and all, but she absolutely pales in comparison to the Heroes pantheon.
Awakenings: Not much to comment on.
>Flandre
AS: Broken as shit. Look at Awoken Shiva's skill to know why. And don't even get me started on the buff dispelling.
LS: Depending on how far the 2x could take you, the 1% constant leech on all attacks could be fucking nuts.
Awakenings: Buffs for sub-colors have been out of the meta for a while. Get rid of the dark orb enhance.
>Remilia
AS: On one hand, it seems broken since it can loop with a friend Remilia, completely removing light from any dungeon, making it easier to beat. On the other hand, that's all that it does.
LS: If she's gonna increase dark orb rate, too, you might as well go the Ilm/Zuoh way and include it in the damage production. Fire/Dark, Fire/Fire/Dark, Fire/Fire/Dark/Dark, etc.
Awakenings: Gimmicky, but not uncommon.
>Daiyousei
AS: Charges a bit too fast, I'd say.
LS: Seems okay.
Awakenings: See the comment on Flandre.
>Koakuma
AS: Reshuffling seems pretty useless.
LS: 30 orbs is the whole standard board. You'd need to be an Anubis autist to consistently achieve that, and x4.5 is a pitiful reward for Anubis-tier skill.
Awakenings: See the comment on Daiyousei/Flandre