Jeanne Ruler!

She's pretty good, as five stars go. Not like Merlin or Waver good tho. Out of an arts stall team, she's mediocre at best, which means you want to pair her with Hans and Mash or similar servants(ironically for you, Merlin synergizes amazingly well with her). Part of the reason why she's so mediocre is her np self stuns. She later gets an interlude that removes this stun(and all debuffs from party), but that's still a ways from now. Stick Vessel of the Saint on her for three free nps.

Not now, but after her NP upgrade she will be very useful. In the future with break bars, it is harder to finish fights quickly in challenge quests so survivability becomes much much more relevant - that's when her lumineru eterunaru shines the brightest.

Take your time to slowly groom her and she will repay you in the future :)