Liino Gear Setup and Skill Priority

Stack Will first and Agility second. Eternal Xiranite Gear Pack 3-piece is the default set.
Stat Priority
Main attribute is Will. Secondary is Agility.
Will feeds Electric and Nature Amp during Cosmovoice Stance. At mastery 3 that is about 0.04% Amp per Will up to 60%, so Will is first for party damage buffs.
Agility scales heal numbers. Take it second when you want more treatment.
Ultimate dependency is high, so Ultimate Gain Efficiency options also help.
Gear Setup

Eternal Xiranite Gear Pack
Hongshan Swordmancers

Eternal Xiranite Gear Pack
Hongshan Swordmancers
Will support gear pack with black tactical armor and mint-green accents from Hongshan Swordmancers.
Run Eternal Xiranite Gear Pack 3-piece as the baseline. Prioritize Will on armor, gloves, and kits. Fill the last slot with Will, Treatment Efficiency, or Ultimate Gain.
This matches Will support Arcane direction, so you can reuse pieces if you already farmed the set.
During progression, any Will-heavy temporary set is fine until you finish Eternal Xiranite.
Weapons
Signature Brilliant Night Debut gives Will, Heal Efficiency, and Medical. That lines up with healing and support.
Without signature, Heyday (Will / Heal Efficiency / Pursuit) is the usual substitute. Both keep Will and Heal Efficiency.
Damage weapons cut heal and Amp value. Keep a Will weapon when she is on support duty.
Skill Priority
Ultimate > Combo Skill ≥ Battle Skill > Basic Attack
Ultimate Dawnstar Concerto holds Electric and Nature Amp plus forced Electrification. Will-scaled Amp also sits on Ultimate, so raise it first.
Combo Delightful Harmonics returns 20 Ultimate Energy (above the usual 10), heals the controlled operator, and arms Starry Boost SP return. Level it next to Ultimate.
Battle Skill Dazzling Focus opens Vocalist Stance, team ATK, and sustained heal. Combo requires that stance, so do not skip it.
Basic Attack comes last.