Caster support

Tamamo is definitely the one to focus on first. She will be the most helpful on your friends list as she is key in fielding an Arts team and with her kit and NP she will help people survive.

As for your second one to push, I would stop on Nito and switch to Helena. Helena’s AOE NP is more powerful than Nito’s. Nito completely relies on the death activating to be effective. Helena also has a better skill kit. Especially her third skill, which raises each party members Arts, Buster and Quick damage for 3 turns! That is a really useful skill and far surpasses anything Nito can offer. I have all 3 myself and I have little use for Nito. Helena clears mobs better and is a valid and good support to boot

Tamamo is a really good support for Arts teams, although in general use she suffers a slight decline. If you do have an effective arts/stall team, she is the best choice to prioritise.

Helena in my opinion is the better generalist support since she compliments any team comp with an NP charge and 3 card buffs, but her skill cooldowns are really long so unless you have them at least at level 6, she will suffer a lot of downtime.

Nitocris is best used as a farmer/wave clearer, and pretty much nothing else, so low priority for her.