This is something I've been thinking about for a very long time. Shade and Ekko's are currently the only two "Spirit" heroes, and so far, the Spirit tag doesn't mean anything (No, passives like Spirit Immune don't mean the hero doesn't take damage from spirits... as funny as that'd be). So here's a though: What if Spirit heroes had their own unique race passive, like how Beasts have Pack Tactics or how Undead are Lifeless. Then, perhaps, we could see more Spirit heroes in the future who would create something like a Spirit team with Shade and Ekko. Here's a couple changes I think would be nice:
Ethereal Essence - A new passive Spirits would all share. Ethereal Essence would grant Spirits full Spirit Immunity (to both damage, and effects), and would heal the Spirit if they are hit by a Spirit attack.
Magical Weakness - I wouldn't dare consider buffing Shade without some sort of nerf to counter it. I think since Kai is a Fast Caster with a weakness to Melee attacks, Shade should be a Fast Caster with a weakness to Magical attacks. Shade would take 50% extra damage from Magic attacks with this passive.
Remove Spirit Immune - Just because Ethereal Essence basically covers that anyways.
Remove Undead - There was an argument a while ago about why Shade isn't Undead but Ekko is, since they're both Spirits. My solution is, make Spirit something totally separate and just get rid of Ekko's Undead-ness. Who honestly uses him on the Undead team, anyways? Sorry if this change would upset some people. I just think it's pointless, and confusing when he's compared to Shade.
Spirit-Energy Converter - Spirit allies will gain +1 energy when hit by a Spirit attack.
Electrotherapy - Ekko will purge 1 debuff from all allies when attacking a Shocked enemy.
Energize - Cooldown should be shortened from 7 to 5.
Thunderstorm - Thunderstorm should be changed to 1) Hit the targeted enemy and then 4 random enemies, instead of just 5 random enemies, and 2) have an energy cost of 6 instead of 8.
Intensify Shock - Change this to a new ability called, "Feedback Bolt", a ranged Lightning attack on one target that deals damage, 2x to a Shocked enemy. If the enemy is Shocked, returns 2 energy to the ability, only. If the target is Shocked and killed by the attack, fully restores energy to the ability, only. It would have an energy cost of 5.