I feel like there is probably going to be a Tira bandwagon pretty soon, and it might be a good idea to learn how to fight her. Since one of my training partners mains Tira, I just wanted to share what I've learned while playing with him so much. Please feel free to correct any misinformation:
Most people know that Tira has two stances: Gloomy and Jolly. First thing to know is which moves can change her persona:
JS 66B BE
GS 66B BE
The main ones you will see are GS and JS B+K. Basically if you hit them during the taunt, they will change personas. Also remember that all of her BEs and Jolly CE will switch her personas. Also a lot of these moves hurt her a little bit. If you get her down to low life you take away a LOT of her options and can be more patient.
So now that you know how to tell what stance she is in, here are the moves I have seen mostly used from both stances
JS AB- A high into a low, can lead into her WR B into updraft for a combo. After the JS AB our 9K will beat her options
JS BB- Just a basic BB attack. AA to interrupt usually works for me.
JS 3B- One of her launchers. Not as good damage potential as the Gloomy launcher.
JS 1K- Pretty slow low that is easily reacted to
JS 66AA- This is a move most people do not really get. It may look safe but it is actually full combo punishable by Leixia with any 3B combo.
GS 6A- General spacing tool. Pretty good pushback.
GS 3AA- Starts mid and ends high. You can aGI the second hit of the string with 4A+B. Works on BE version as well.
GS 3B- Launches higher than the Jolly version, which leads to higher combo damage.
GS 4B.B.B(Just)- A launcher that also switches her stances. The last hit is super unsafe though.
GS 66A- Guard break attack with good knockback.
GS B- Three hit attack, pushback on block. I found that a 6KK will stop most of her options, but maybe that was just my friends options.
I think the key to really fighting her is knowing which stance she is in and what moves she can do from it. I like to play semi-aggressive against her, and make sure to punish when I can. If you know she is in Jolly most Tira's will try to get into gloomy, so watch out for the change persona moves. Like I said above she can't really switch stances without hurting herself, so if she is almost dead you limit her options a bit. Spacing her out may be kind of hard because she has good range on a lot of her attacks(GS 6A for instance). If she goes into Updraft without hitting she can cancel into a roll that puts her fullscreen away and makes the move safe.
That is all I can think of for now. Just thought I might get a little discussion going, again please feel free to correct any misinformation in my post.
JS B+K: If you're just randomly using gentle pokes against Jolly Tira, you're going to have to contend with this. It does pose slightly more of a threat to Leixia due to her lower damage, but if you use non-poke moves more than pokes you'll probably just end up with Tira going "COMI--Oh! Ahhh! NOOOOOOooooo!" instead of getting a bunch of meter off of you.
GS 11*44*77A: Any remotely competent Tira player will only be using this at near yellow health to avoid being stuck in Jolly when you inevitably push them that much lower. You'll need to knock her out of it though, it has reasonably high chances of shifting to Jolly on hit, block, *AND* whiff. It does have decent damage, but it's the near-low health persona shift that will be the real problem.
GS 66B*66bA+B+K*66B*66bA+B+K: You're unlikely to see this unless you're knocked down or the Tira player is an idiot, so most of the time you'll have very little(or even no chance) to escape it. If they do use it randomly or as oki though, it has practically no tracking. Mild good news though: if the Tira player's execution isn't up to snuff, adding in that extra 6 for more damage may cause them to drop their combo.
GS B+K: Don't use reactable mids randomly. Do, and you'll be losing 50-65 health while she's enjoying cutting yoru throat so much she gets off and actually recovers a teensy bit of health. You don't want that, as I hear ejaculate from the malfested is pretty nasty...
GS 4B :B :B : It is slightly slower than GS 3B(i19 if memory serves) and has no TC properties, but will deal slightly more damage with its combos than GS 3B combos. It can be stepped.
JS 11*77B: It's kinda wacky, but if it's a CH it's a launch into JS BT B+KB. And with persona shift, you get to deal with the launch into GS B+K into GS 44B or GS 666bA+B+K...Which is very painful. Another big thing is its large TC window and how it puts Tira into a FC state.
JS 2AB ~ A+B: Unless they're trying to be Decopwn Jr. and really messing with your head(or are just really really bad), no Tira will use this string due to how unsafe it is and how JS 2A is pretty damn slow for a 2A. Unless they get a CH on the first hit, they'll only do followups if they're incredibly stupid or messing with you. Think of it like Mitsurugi's 2KB with an aGI followup, it's kind of like that except Tira has little reason to use it. Kick her in the shins to knock her out of A+B and they really have no reason to use the move.
JS B+K: While Leixia does need to worry about this move more than most characters, if you focus on lows and moves that have knockdown/launch/stun properties on CH you'll basically have no need to worry about it. If you keep using your AA BEs and other strings with low damage but no knockdown/launch/stun properties, sooner or later she'll do this and get a buttload of meter from it. If that happens, throw the bitch immediately because you've put her into a nasty aGI state that results in GS B+K's throw and she has the option of canceling with a headbutt.
A+B: This move is kinda bad honestly. It has a decent-sized aGI window and may give her a persona shift, but the aGI window ends when the actual attack part begins and she can't cancel. Do note though that the chances of a persona shift are higher when it hits you(guard or otherwise) and she has the option of adjusting for one, two, or three hits with chances of persona shift(and self-inflicted damage) increasing with each additional hit.
BT A+B: This will never, ever be an issue. If they do this, they're messing with your head or desperate for a persona shift at all costs. Don't let them mess with you.
UD: It's unlikely a decent Tira will use UD out of CH launch combos(like 9K CH), but if they do it's easy enough to deal with. Learn how the spacing is with the 7, 8, and 9 inputs and know in the start of it if you're close enough to dash forward under her. UD A is the only move out of this stance that can't be sidestepped, UD B will only be used if they intend to get behind you, and UD K can hit low with a stun at tip range. UD K is the big threat due to it's tip range stun and the inescapable followups period. All three attacks in UD hit at about the same time(except K's low hit at tip range), so if you feel up to it JG and GI will make her regret being so foolish.
JS 66bA+B+K: You'll only ever see this in combos, whiff punish, and as oki. It's just too slow and unsafe to use otherwise. It has decent tracking and launches downed foes though, so you'll generally want to ukemi and block immediately if JS Tira knocks you down.
GS 44B: A meterless move that can deal 70 damage and BUILD meter. Block it. She can delay it almost a second for more damage, but she can let loose when she pleases. It's also a go-to substitute for GS 66B for ending combos, dealing no self-inflicted damage and building meter instead of burning for a single digit difference in damage. Learn this move ASAP, avoid the instinct to crouch it as it hits mid and mid only.
BT state: BT 2K, JS BT B+K B, and GS B+K are prime tools. GS B+K leads to the launch combo of Tira's choice and the aGI on it is pretty damn nasty...Good luck?
inb4 someone actually good gives much better advice