Tanjiro had free access to the STW as soon as he inherited his ancestor's memories and kept it on constantly until fatigue hit him, it's now a passive buff to his speed which can be maintained as long as he isn't extremely fatigued and injured, additionally, he also goes for it against dangerous opponents which deku absolutely is in this case, and i never argued it was vastly superior to faux 100%, merely that with it, in addition to the breathing form amps, his preception enhancement ie seeing deku in slow motion, superior skill and precog he would have the definite advantage in his fight against deku.
Tanjiro only used it on-and-off, but either way it's not opening move and he won't be using it for long either. The 5x multiplier from Fa Jin, on top of his increased power from kicks + Deku greatly upscaling from his 2.15 Megatons value = Tanjiro not walking out without a serious injury. Plus, again, Deku can also just counter Faux 100% to either match or surpass his speed and hit him with an AOE shockwave that would be virtually unavoidable. And again, stacking that with Quintuple Recharge is definitely putting Tanjiro in critical condition.
the breathing forms can be used almost instantly, the speed of their implementation is vastly faster than the slayers' own movement and attack speeds, seeing deku here is at best equal in speed he wouldn't be able to react to it even if he felt it and knew it was coming due to danger sens since he wouldn't have the speed required to react even if he knows it's coming, and even assuming he could, tanjiro sees him in slow motion and adjusts his moves to where he could potentially dodges by watching his muscle movements so his attack hits him
The breathing forms can't be used to amp speed or AP here, because except dancing flash, nothing else is listed on his profile. I just gave you the benefit of doubt and said Fake Rainbow worked as teleportation to avoid the bad profile argument. But either way, that's not happening. Danger Sense would detect Tanjiro the moment he takes a breath to use a technique, and with Deku's foresight-level prediction he'd have no issue dodging. Also worth noting that it's not in character for Tanjiro to use the STW off the bat.
nichirin swords suffer from anime mineral syndrom wherein they somehow get more durable with skill, they're fragile enough for inosuke to break using a random rock off the road yet you can use them to cut materials several orders of magnitudes more durable than even steel without them breaking apart
Point is, swords have been broken before, and Akaza could shatter Giyu's sword with a well-timed tap on the dull-side, without even using a BDA. Deku's smart, he's good at timing, and he has more than a 5x AP advantage here, that sword is not surviving a direct strike from Deku with Quintuple Recharge.
tanjiro also has the ability to deflect one shot tier attacks with his sword in a vastly less skilled key (season 2 against gyutaro's blood blades)
Tanjiro deflected blood blades once from a non-trying Gyutaro, and again from a poisoned but recovering Gyutaro near the end. Plus both times were against projectiles. Worth mentioning the fact that Nichirin clearly has negative effects on demons and their blood demon art. Zohakuten's lightning poofed away when Mitsuri slashed through it, Akaza's shockwave projectile thing disappeared when Giyu slashed it in half, Rui's webs disappeared off-camera after Giyu cut them, and Kokushibo straight up stating he couldn't Gyomei's change due to the high amounts of sunlight it had absorbed.
so even if for whatever reason he didn't have the time to think of countermeasures to dodge the attack in his slow mo world, predict deku's movements with precog or do anything and somehow still get fist to make contact, he can simply divert it or use his breathing forms or teleportation to get out of the way and slash deku's head, before he could react
If he's getting blitzed by faux 100%, then he's not gonna have time to use a breathing technique. Same thing happened with Akaza when he teleported behind Tanjiro, and with Gyutaro twice when Tanjiro couldn't use a technique fast enough. Those things can be activated fast, but not instant. Also the STW is his highest amp and the breathing techniques don't stack on top of it.
temporary but more than enough to land a decisive blow on deku, his speed amps are taken into account here since their speed is relative with both faux 100% and STW active, tanjiro can stack the breathing amp forms on top of that giving a decisive speed advantage
Tanjiro can't stack breathing techniques on top of the STW. Look at his profile. And either way, it's just a matter of who activates their blitz amp first, with Deku having a slight favor with the 5x AP increase likely leaving Tanjiro in critical condition even IF he blocks.
and i don't think it takes a lot of intelligence to realize taking a sword away from a swordsmen is a pretty effective move...problem is doing it, and i highly doubt deku just yoink the sword from tanjiro's hands, he can try but he will just fail miserable, and i'd say their BIQ is about equal seeing tanjiro's track record of doing stuff like analyzing akaza's bda based on subtle clues, analyzing his opponents and their weaknesses, creating fighting styles on the spot, etc
I'm just emphasizing that Deku is a quick thinker and strategic fighter, taking the sword out of his hands would be his first priority. And either way, snatching it wouldn't be pretty hard, considering he has a massive LS advantage and he can use his blitz amp back-to-back. Even if Tanjiro can block the attacks, Deku can literally just snatch the sword out of his hands. Also HIgh 6-A gauntlets. Tanjiro's not gonna deflect that shit.
bro stop pretending we know it's you
<3