This is a oneshot, and it's pretty charming.
Frederica Lumina Rosalin
Frederica is incapable of dealing damage; all of her attacks instead target an ally; 10 or lower is a failure, but above heals 1d6+half support stat to said ally. 20+ heals 2d6+HSS.
When an opponent makes an attack that rolls less than (Frederica's attack stat + 3), they instantly drop to 0 resolve.
Luminescent Triad: Make a challenge in attack, defense, and support, respectively. All opponents may defend against the attack roll, and on failure take damage equal to Frederica's attack stat; on success they take 1 damage instead. For the defense roll, every 2 over 10 becomes a static number added to the defense stat of all allies for the next turn. For the final roll, with support, all allies heal (number rolled/10) resolve. Overcharge may be taken on each one, and all are rolled in the same turn. Frederica may not act on the following turn.