I had a much larger writeup for this build previously... but ultmately I think it was mostly meaningless, unnecessary fluff (especially if TAHITI really is going to be recieving a "balance patch" at some point down the line which could render this entire build outdated anyway)... soo I deleted all of it. If you were someone who liked or got use out of that old rambling writeup sorry. This build is so simple by design that I think an "in-depth guide" is totally unnecessary. I am going to leave my thoughts on some of the gear choices, because I think not all of it speaks for itself and/or might need further explanation:

About Catalyst Invisibility:  I only gave this a passing recommendation as a nice but ultimately not required bonus in my previous writeup that I deleted. But after much more time and experience over these past few months piltoing this build through TAHITI's frequent hiccups and server de-syncs I'm ammending my old advice. In my current opinion, an invisibility on medkit catalyst is borderline MANDATORY if you want this build to function as advertised. I think it's so important I'm moving this particular section to the top above everything else to make sure people see it. The main reason I think it's so necessary is the repellant garbage known as "cosmic bulwark", an affix that the bosses you'll be targetting can arbitrarily roll every terminal instance/reset on cosmic difficulty. If the boss has it, no amount of DPS you have will be enough if it happens to activate before your signature finisher. And believe me it will, and it will drive you crazy while ruining your fun and farming efficiency over the long haul if you let it. Thankfully, invisibility on medkit DOESN'T let it happen; if a boss is unable to target you and isn't aggro'd, then they're also unable to activate annoying affixes like bulwark or vaccum as they're technically not considered "in active combat". For this reason I'd recommend not deploying an active teamup on this build, and popping your medkit right before you engage the boss; do this correctly and they'll stand in place cluelessly, allowing you to easily line up and fire   with no risk of interruption. It takes a tiny bit of experience timing it correctly for each specific boss/terminal layout, and reliably having it off cooldown depending on stray enemy fire on your way to the boss. But you'll get the feel for it before long. 

 No, this isn't a mistake or a meme. What it IS is probably the most underrated and/or slept on unique in the entire game. Do you see those outrageous critical and brutal damage rolls?? They are in fact HIGHER than those found on the "best item in the game", good ol'  for anyone keeping count!! Yes, Fragment has considerably higher base damage and sizable TTL utility compared to... nothing of the sort on the ammo. But what these pointy bullets lack in survivability, they more than make up for with an unconditional vulnerable on hit property, the very same as the oft recommended  in slot 5. For our auto-brut, terminal boss one-shotting purposes... it is actually optimal to drop Fragment in slot 1 in exchange for being able to drop a vulnerability power from our skill "rotation" (if you can even call it that at this point LOL), bringing it down to nothing but popping  followed by popping the boss. I personally slot  purely for mobility purposes; the vulnerability application when killing bosses comes from the ammo in slot 1. 

 Yes, they're BiS for Blade, they aren't for any other hero (outside of outlier IP brutal fishing for a TTK on the raid dummy). This is a meme/trap item on basically every other hero in the game, including Mr. Fantastic positron emitter builds. But for a canonically shades-wearing Dhampir, who scales off Fighting, and has a massive auto brutal signature, they're an exclusive match made in heaven. Steer clear of  and  , these are NOT "BiS" by any estimation and should be actively avoided on Blade. 

 This prooobaby isn't better than  , I'm pretty sure the only hero it's unarguably BiS on is Taskmaster. But it's close, SHIELD agent medalions are in high demand on basically every other fighting hero in the game, and I happened to have a near perfect rolled spare of this lying around so I decided to list it for this build's purposes. Blade's the only other hero in the game besides Taskmaster who can make use of this medallion because of his particular main stat typing and his auto-brutal signature finisher. Something to keep in mind depending on your cosmic reliquary luck. 

A cosmic  could end up being a bit better than  considering we aren't building bloodlust and won't reliably if ever be starving when engaging terminal bosses depending on layout. But it'll need to be well-rolled to measure up, and isn't a requirement by any means.

Finally, for the insignia: yes, brutal damage is technically poor value for it's stat weight here. But Blade's signature finisher skews that calculus a bit; if you happen to have a god-rolled Crit/Brutal damage insignia this is one of the ~3 heroes it can find a good home on IMO. Crit or brutal strike in it's place are good as always. As for the artifacts, there's multiple viable options and replacements for what's listed. Something like  isn't BiS from a pure damage perspective, but was chosen because of the lack of conditions for most of its stat bonuses. You want to avoid things like  which might appear strong and synergistic for Blade on-paper but lock the majority of power and functionality behind conditions like "on bleeding enemies" that will unnecessarily lengthen our "skill rotation". Remember, this ISN'T the highest damage Blade build possible by any means. We don't talent or build bloodlust at all, how could it be? Once you have enough damage/IP/ultimate upgrades to guarantee oneshots with the signature, everything else is about reducing the hassle and steps necessary to achieving that, not adding to it. ;)