Yomi

Depressed

Middle row

Magic damage

Mystic

Support

Moonflower

Summons a full moon that shines down on the ally with the highest Max HP for a set period of time. Increases Defense of allies bathed in moonlight and reduces Attack of enemies under the moonlight. During the time when there's moonlight, Yomi's Basic Attacks become Enhanced Attacks.
■ Ally DEF increase: 31%
■ DEF increase duration: 6s
■ Enemy reduced ATK: 41%
■ Reduced ATK duration: 6s
■ Moonlight duration: 8s

Devoted Reception

26 sec Cooldown

Summons a moonlight walking on clouds for a set period of time. The moonlight slowly advances in the direction Yomi is facing. Allies within the moonlight recover SP every second. Deals Damage to Enemies every second and reduces their SP.
■ Ally SP Recovery: 15
■ Magical DMG per sec: 470%
■ Enemy SP Reduction: 20
■ Moonlight Duration: 12s

Passive

Increases HP recovery for all allies. (This effect activates even if Yomi is not on the field).
■ HP Recovery Increase: 23%

Normal ATK

Casts a spell, dealing Magical Damage to the enemy
■ Magical DMG: 60%
Enhance:
At a set chance, drops starlight to deal magical damage to 2 random enemies and reduce their attack speed. Additionally recovers own HP and that of the ally with the lowest remaining HP ratio
■ Magical DMG: 300%
■ ATK SPD Reduction: 40%
■ ATK SPD Reduction Duration: 3s
■ Own HP Recovery: 16% of Max HP
■ Target HP Recovery: 16% of Max HP

Skill priority

You will level up most skills regardless how useful they are for the combat power padding in endgame. As a general rule of thumb:

Units you are not sure you will use long term: Skills to level 4. If they're passives that benefit the team, can take that to 7.
Strong units but not your main personality: Skills to level 7 for raids and elemental content. Not worth going higher if they are not your main team.
Strong units on your main personality (and waifus): Max out skills. You can start with 7/7/7 and slowly work towards 12/12/12 when you can sweep stage 10.

Recommended artifacts

Artifacts and runes will always change depending on the stage and content you are currently facing, this is just a couple of examples on what items work for this Apostle.

Legendary