Warframe

So after a lot of playing Koumei this is a series of tricks, some obvious and some hopefully not, that you can use to get the most out of her kit. I'm going to try and format this thing into sections but I was never the best at typography so hopefully the end result is coherant.

The goal of this guide is not to build around specific decrees but instead to allow her to directly benefit from as many decrees as possible and thus reducing the rng element.

--Koumei herself--
So there's a few things you can do on Koumei herself to make life easier, most of these are pretty well known but I'm including them for the sake of having a comprehensive guide.

• Sickening Pulse: Probably the most well known Helminth for Koumei, its popular because it works, synergizing with her 4 to allow for nuking all the way up to level cap, this buff to her 4 also makes several decree challenges much easier.
• Parkour mods: I know a lot of people hate the idea of wasting an exilus on this but it really does make her gameplay that much smoother, something in the lightning dash family of mods is ideal and once you start the extra bullet jump distance is hard to give up.
• Armor: This is more than just defense for Koumei, in long runs it can also translate directly into power strength, and with arcane battery a mod like umbral fiber can sub in for (primed)flow too. A full Umbral Koumei hits a permament 600% power strength once her decrees are stacked.
• Equilibrium: Another useful but niche option, Koumei has decrees that both create and benefit from health orbs and this mod synergizes well with them.

--Decree challenges--
Some decree challenges can be a pain but with the minnimal investment of sickening pulse (and maybe that parkour mod) most of that pain goes away.

• Kill X enemies afflicted with element: Basically free, if its not one your weapon just prime with your 4 or kill with your 4 + sickening pulse, or with whatever weapon your passive is on right now.
• Kill while airborne, sliding or wall latched. Cast your 4 when on the ground, then do the appropriate manuver and hit sickening pulse, works everywhere from base level to endurance. Alternatively shotguns can do this a little slower but are less finicky, especially with sliding.
• Headshot kills: This is actually the only challenge I routinely skip, you can make it easier with skill or specific weapons but weapons that work best with Koumei tend not to be the greatest for headshotting and one of your own decrees can actually steal your own headshots by turning them into toxin procs.

--Equipment--
Koumei is in many ways a weapons platform frame, however unlike frames like Rhino, Mirage or Saryn the buffs she provides are less clear cut; in her hands some weapons hardly benefit at all while others can achieve heights far above what can be achieved with more conventional buffs.

• Hybrid: This is the most basic rule of gearing Koumei, decrees benefit both crits and status so a weapon that inflicts both is going to get the most consistent benefit.
• LMGs and Shotguns: A large number of her less popular and thus wasted decrees relate to magazine capacity, ammo efficiency and reloading. With many weapons these are useless, with the right weapons they can be excellent. Both weapon types tend to suffer from long or frequent reloads, delaying or skipping these alone is a nice buff. LMGs in particular have huge base magazines which can reach or exceed a thousand capacity with the right decrees, this can turn into truly bottomless magazine with reload on kill or even an additional 1000% electrical damage. Shotguns are similar, with magazine capacity, ammo efficiency and reload decrees allowing them to function as bullet hoses, its less dramatic than with LMGs but you haven't lived until you've tried bottomless magazine Felarx.
• Melees: Another way to put the initial summary of this section is that Koumei is a jank amplifier. dual ichor and okina incarnons are already strong but the daggers and clouds proccing decrees on their own is a whole new level of crazy. Projectile weapons go crazy with multiplicative CO and the inevitable melee rainbow status you aquire (even without priming). Heavy attack crit weapons make an entertaining alternative to hybrids with their own set of decrees that turn everything into a corrosive syam. Of course if you can get a fun hybrid heavy attack weapon then that's the dream and please mention it in the comments.

--Specific gear reccomendations--
Just some gear for Koumei that's effective and fun, and most importantly helps avoid wasted decrees.

• Trumna(prime): Its no torid incarnon (what is?) but as far as Koumei primaries go this has it all. At the start of the mission is a solid hybrid LMG with an alt-fire that can really come in clutch when you're having trouble with those airborne/latch/slide kill challenges. Stick around for a while and its an endless stream of bullets with all the fire-rate and damage you'll ever need.
  -Quellor: A side-grade to Trumna that trades damage for being a bit more consistent with headshots, and trades the grenade for the alt-fire that opticor wishes it was. Also has the highest base magazine capacity in the game if you really want to make the most out of the magazine size to electrical damage decree.
  -Scourge(prime): Largely a utility pick for the headshot challenge but also a decent weapon in its own right, most decrees just help this keep up with level scaling but if you get the ones that inflict toxin and electric AOEs on headshots then this thing is suddenly a rapid fire rocker launcher.
  -Shade(prime): At low levels this plus verglass or primer of your choice can help with damage CC or whatever you need. Into endurance (or right away if you want to build for it) you almost certainly have enough strength and efficiency from decrees that you can just sit around invisible and spam this + sickening pulse to nuke everything without even being shot at.