Ability Breakdown:

[Nezha]'s playstyle is pretty straight forward, but effective if done right.

[Firewalker] (1) should be used when you want to move fast, or lock out an area from the enemy (such as defence missions). its also capable of removing status effects from allies, though with [Safeguard] doing the same, its of minimal use. This is a great helminth slot

Blazing Chakram (2) serves three purposes. the first is teleporting - press once to throw, and again to teleport to the chakram. the second is debuffing; any enemy hit by chakram will take more damage, equivalent to your ability strength. great for demolishing demolishers! Third is spawning health/energy orbs; debuffed enemies are guarunteed to drop orbs when they die!

Warding halo (3) is your most important ability, as its what keeps you alive. Cast it on allies to offer them the same benifits; status immunity (includng knock back!) and huge amounts of DR

Divine Spears (4) is your CC ability. its range is decent, even with neautral range, and can lock down a lot of enemies. throw a chakram at one to cause it to split and hit them all, allowing for a weapon AOE nuke followup.

The stats logic:

[Nezha] prioritises strength above all else, but wants to maintain as neutral as possible on duration and range.

Why? Warding halo, and blazing chakram

Halo is your survivability - the higher the strength, the higher the effective DR due to the armour multiplication it provides.
Chakram is your vulnerability booster. As we lack an armour strip here, chakram offers a way to deal massively increased damage by making the enemies take more damage. With 408% strength (after arcane boosts) you're essentially doing 408% more damage to anything debuffed with chakram

We want to keep a neutral range to ensure that spears can still lock down a reasonable area if needed

Molt Efficiency brings us back to 100% duration, which is more than enough. Spears stits at the 12s mark, and the chakram debuff at 15s which i find to be enough. If you feel duration is not sufficient, you can swap [Augur Secrets] for [Augur Message]. If you want even more duration, instead swap [Transient Fortitude] for [Primed Continuity] (though i find this to be overkill)

Arcanes:

You can run energize if energy is a concern, but Molt Efficiency is the better choice in my opinion.
Arcane [Guardian] can boost warding halo, because it increases the base amount of health your halo gets, reducing the frequency at which you cast it. Use this if you're not comfortable building large halo pools

Molt Augmented is a great addition for [Nezha], giving a bit of scaling to both halo, and chakram as you get kills, and is mandatory

Mods:

[Umbral Fiber] and [Umbral Intensify] are important here, as they feedback into each other, with both contributing to halo.
note: i see some builds running [Umbral Vitality], or [Archon Vitality] instead of umbral fibre. The fact is, between [Adaptation] and Warding halo, you have so much EHP (and charkram guarunteeing health drops) that the extra health is pointless. As halo scales with armour, you effectively double dip on the DR. Don't fall into that trap.

[Flow] is needed to counter the negative efficiency from [Blind Rage], and enable you to maintain warding halo when it drops, whilst comfortably throwing out chakrams. You can drop [Augur Secrets] for [Streamline] if you find energy to be a problem, but honestly the extra drops from chakram makes it not needed, especially if running energize

[Blind Rage] and [Transient Fortitude] are adding to our total ability strength which as stated, is [Nezha]'s most important stat. The negative duration (if efficiency drops) might seem off putting, but even an 8s spears, and 11s chakram debuff are more than enough. If they're not, you have bigger problems!

[Adaptation] is a big help for [Nezha], taking his DR with halo from 90% to over 99%. This results in an EHP in the millions. [Rolling Guard] might be tempting here, but halo already covers the debuff portion of it, and anything that will cause you to use its invulnerability will likely drop halo as well, which comes with its own invulnerability. All this makes [Adaptation] is the better choice imo.

You can run cotrolled slide in place of [Power Drift], as it provides the same amount of ability strength. i personally make use of nezhas passive, so prefer power drift, but each to his/her own

[Safeguard] is a flex slot, but can be a real nice to have in groups, allowing you to increase ally EHP by a large amount. It can also be cast on a lot of defence points, as well as companions, further increasing its usefulness. [Equilibrium] can be slotted here instead for more energy, but requires an additional forma

Archon Shards:

The increased debuff on chakram from the red shards is nothing to sniff at and for tha reason, i'd suggest prioritising reds set to ability strength

A single violet shard focusing on health/[Energy Conversion] is a big addition, due to the sheer number of health orbs halo generates

Blue shards may be tempting, as the armour increase impacts halo more than ability strength. Throw one in if you're concerned about survivability but honestly, its not needed

Helminths:

You can swap [Firewalker] for wukongs defy for more CC, and an even stronger halo if you want more survivability (as the armour value is added to halo's multiplier at the start). Once you're comfortable building large halo pools however, this falls off quickly in value

You can also swap [Firewalker] for Grendels Nourish, for more energy, as well as viral procs. I would personally recommend as a minimum swapping [Augur Secrets] for for message if you do