Hello everyone,
I'm a [Nezha] main for some years now and thought I could share my builds aswell. Please notice that [Nezha] is a highly versatile warframe and these builds work for me and my playstyle, but might not fit yours. Okay, let's start!

General Use

This is my general use build with a good balance in stats and utility for survivability, damage and fun. It works for enemies and missions at all stages of the game, including Open World and Steel Path.

Difficulties

• 2 Forma
• 2 Umbral Forma from Nightwave or The Steel Path Honors Shop
• 1 Aura Forma from Arbitrations (Rotation A: 1%, Rotation B: 2%, Rotation C: 4.5%)
• Augur Secrets from Cetus Bounties (30-50-3 Rotation B: 2.08%, 30-50-F Rotation B: 4.76%)
• Adaptation from Arbitrations (Rotation A: 2%, Rotation B: 2.5%)
• Equilibrium from Lephantis (Head) (7.52%)
• Transient Fortitude from Orokin Vaults (Rotation A: 4.35%)
• ~248k Endo in total

Variations

• Controlled Slide instead of Power Drift
• Stretch, Augur Reach, (Primed) Flow, Natural Talent, Safeguard or Reaping Chakram instead of Augur Secrets
• (Primed) Flow or Streamline instead of Equilibrium
• Energy Conversion instead of Primed Continuity
• Blind Rage instead of Transient Fortitude
• Archon Vitality instead of Umbral Vitality

A big variation:

• Move Adaptation to where Umbral Fiber is and
• Narrow Minded instead of Umbral Fiber and
• Blind Rage instead of Primed Continuity and
• Fleeting Expertise instead of Equilibrium

Possible follow up variation:

• Controlled Slide instead of Power Drift and
• Move Fleeting Expertise to where Augur Secrets is and
• Equilibrium instead of Augur Secrets

Aura

• [Brief Respite]. [Nezha] doesn't rely on Shield Gating as much as some other warframes do, but it's certainly an option. Don't forget to equip a Decaying Dragon Key to reduce your shield by 75%. Also consider modding for negative Ability Efficiency by using Blind Rage.
• [Combat Discipline]. In combination with Arcane Avenger, you have a 21% chance for +45% Critical Chance for 12 seconds whenever you make a kill.
• [Corrosive Projection]. Not all enemies possess armor, but the ones that do are considered the toughest. This aura has no effect against most Corpus and Infested.
• Enemy Radar. Seeing enemies on the Minimap is always useful and a utility often favored over increased damage.
• [Growing Power]. All of [Nezha]'s abilities use Ability Strength. Also, [Growing Power] doesn't have a limitation on how often it can be triggered, so likely every use of Blazing Chakram will be buffed by this mod as long as you use a weapon that can inflict status effects quite regularly.
• [Shield Disruption]. If you don't carry a weapon with Magnetic damage, dealing with shields can be a difficult task. Consider taking this mod if you play against Corpus as most of them have a shield.
• Speed Holster. If you like playing with and around your primary and secondary weapon, this is a great aura to help with that playstyle.
• Sprint Boost. More fast.
• [Steel Charge]. This is a great aura if you primarily use melee attacks. [Steel Charge] also increases your mod capacity more than most other auras do.

Companion

Take whichever you like. I fell in love with my [Smeeta Kavat], but any other companion works aswell. If you play with a sentinel, consider using the mod [Safeguard] to [Protect] it.

Focus School

After the Focus School Update, Unairu seems like the strongest focus school. However, I like using and playing around energy as much as possible, so I tend to use Zenurik on most frames.

Arcanes

There are a lot of arcanes that work well on [Nezha]. Take whichever you own and like.

Helminth

[Nezha] has a nice kit on his own. There are a lot of helminth abilities that work on [Nezha], but most of them alter this build to some level as you can see in my other [Nezha] builds. For this general use build, I'd keep [Nezha]'s abilities. If you choose to run the big variation from the section Variations, you effectively don't have any range anymore and I'd recommend infusing something over [Nezha]'s 4 that relies less on range.

Archon Shards

Archon Shards are a great way to complement or supplement builds.

Generally useful:

• Crimson (red) Ability Strength. All of Nezha's abilities scale with Ability Strength, so having more Ability Strength is never a bad idea.
• Azure (blue) Energy Max. Complementing Nezha's relatively low Energy Max with Archon Shards reduces the need of using (Primed) Flow.
• Amber (yellow) Casting Speed. You will and should spam [Nezha]'s 2 a lot. Having some additional Casting Speed makes it less tedious and redueces the need of using Natural Talent.

Niche:

• Crimson (red) Melee Critical Damage. If you use melee a lot, more Critical Damage is a great boost in damage.
• Crimson (red) Primary Status Chance. If you use your primary weapon a lot, procing more status effects is useful for every weapon.
• Crimson (red) Secondary Critical Chance. If you use your secondary weapon a lot, a higher Critical Chance can mean the difference between yellow and orange or orange and red crits.
• Amber (yellow) Parkour Velocitiy. [Nezha] already is quite mobile, more Parkour Velocity feels great!

Q&A

1. Why [Umbral Fiber] instead of [Health Conversion]?
   I know there is a large debate about [Umbral Fiber] and [Health Conversion]. I actually use [Health Conversion] in another build. Thing is, [Umbral Fiber] not only gives +192.5% Armor together with [Umbral Intensify] and [Umbral Vitality], but also adds +22% Ability Strength to [Umbral Intensify] and +220% Health to [Umbral Vitality]. With that in mind, one could even argue that we don't need [Augur Secrets] in this build anymore (besides from its set effect) as we already roughly get the same Ability Strength through [Umbral Fiber].

2. Why not [Blind Rage] instead of [Transient Fortitude]?
   There are basically two reasons to (further) increase Ability Strength: a) The Damage Vulnerability from Blazing Chakram and b) The Absorption Multiplier from Warding Halo. [Equilibrium] makes it possible to equip [Blind Rage] without having too big energy problems. If you feel like you have energy problems, use [Streamline] instead of [Augur Secrets]. The actual problem is the second Madurai (V) polarity. If we don't use [Transient Fortitude], [Primed Continuity] isn't really needed. But what do we do with that slot then? The only options I could see are keeping [Primed Continuity] anyways, [Energy Conversion], [Speed Drift], [Cunning Drift] or a mod that lacks the madurai polarity, but is cheap enough to still fit in. Personally, I'd just stick with [Transient Fortitude] and forget this problem or use the big variation from the section Variations.

3. Why [Equilibrium] instead of [Hunter Adrenaline]?
   I feel like in most content I don't take enough damage on health to justify the use of Hunter Adrenaline in a General Use build. Energy- and Health Orbs drop everywhere, especially enemies affected by Blazing Chakram, so we can make constant use of [Equilibrium]. [Equilibrium] also has a great synnergy with [Combat Discipline] as we can always pick up Health Orbs, meaning more energy thanks to [Equilibrium].

4. Why do you call this build "Endgame"?
   I call this build "Endgame" because of all the difficulties of this build, which you can see in section Difficulties. Even if we ignore arcanes, you still need 248k Endo, 2 Umbra Forma and several more or less rare mods. If you have the resources for this build, you are in my eyes in the endgame of this game. Notice that this build isn't meant for level cap endurance runs.

Updates:
15.04.2023 Formatting
02.01.2023 Added the section Archon Shards.
22.09.2022 Added (Primed) [Flow] as an option in section Variations.
13.09.2022 Added [Archon Vitality] as an option in section Variations.
15.07.2022 Updated the Q&A section.
25.06.2022 Got rid of the Purpose section, updated the Difficulties section, (finally) switched [Corrosive Projection] to [Combat Discipline].
24.06.2022 Added the section Aura and made some minor updates to some other sections.
22.06.2022 Updated the Variations section by adding [Natural Talent] and [Energy Conversion] and added a new subsection in the Q&A.
25.04.2022 Updated the Variations section and the Helminth section accordingly.
12.04.2022 Updated the Q&A section.
07.04.2022 Switched [Primed Flow] with [Equilibrium].