Precognition:

When any ally loses HP, accumulate [Bloodtithe].

I1:

When Rubuska is on the field, grant all allies [Shadow Playmate]. Whenever any ally's [Shadow Attire] reaches its maximum stacks, Rubuska's moxie increases. Self excess moxie will be temporarily stored and, if Rubuska has available capacity at the end of the round, it will be replenished.

I2:

When entering battle, increase Max HP.

I3:

When entering battle, grant all allies [Blessing of Rubuska the First]. Whenever any ally is attacked, Rubuska heals all allies.

[Shadow Playmate]: At the start of the round, lose a certain percentage of current HP. A portion of the HP lost by Rubuska through this effect is converted into [Shadow Attire]. When Rubuska leaves the field, [Shadow Playmate] is removed.

[Shadow Attire]: Increase the character's Max HP / Crit DMG / Ultimate Might based on [Shadow Attire] stacks.

[Blessing of Rubuska the First]: When the bearer takes lethal DMG, they will not leave the field and instead heal their HP.

Arcane Skill 1: Midnight Prank
1-target attack, lose a portion of current HP to deal Reality DMG. This attack counts as a [Retribution]. Increase the [Shadow Attire] stacks of all allies who have [Shadow Playmate].

[Retribution]: When attacking, DMG is scaled with 20% of self max HP instead of ATK.

Arcane Skill 2: Shadow Guards
Mass heal, restore HP to all allies, cannot crit; increase the [Shadow Attire] stacks of all allies who have [Shadow Playmate].

Ultimate: Victory Belongs to 'Rubuska the First'!
1-target buff, target enters [Shadow Feast], and heals all allies.

[Shadow Feast]: Drain all [Shadow Attire] from allies other than the target. The target gains a portion equal to the sum of the drained [Shadow Attire]. The extra [Shadow Attire] provided by this status does not affect the target's own [Shadow Attire] gain and can exceed the normal limit. The Crit DMG / Ultimate Might gained from the extra [Shadow Attire] is slightly lower than normal.