Kasumi is a high tier character. Just like in previous DOAs, what stops her from top is her safety issues. Anything after her initial pokes she is screwed. Her holds outside of advance mid-kick or her low kick hold she does mediocre damage, even on Hi Counter. The majority of her throws are still slow. Her NH damage is fairly weak from her throws to juggles. She is very limited at long range so at the back of the screen she loses fights easily. Personally I have no problem at the back of the screen with Kasumi and I will not lose easily because it. However, tool-wise, Kasumi doesn't have too many things that will allow her to close a long distance gap. These are things that prevent her from being top tier.
What definately makes her high tier is her ability to play the stun game and punish holds with launching throws taking a quarter of your life no matter which throw Kasumi uses. That's 100 pts of damge on Hi Counter, Kasumi throws you 3 times and the fight is over her Hi Counter throwing you. Now, with the new system mechanics Kasumi does not have to rely solely on that gameplay, the stun game. Kasumi has the ability to bypass the stun game for guaranteed damage and that damage is almost taking a quarter of life. The damage ranges from 71-93 pts of damage (it will take a quarter of life on Hi Counter hits), that damge is for both of her moves that allow her to bypass playing the stun game.
The first move is H+K followed by 6K ( I invented this shit FYI), this move is 17i, hold resistant (she takes no damage if you hold it) , she has follow ups from it so holding it isn't end all be all, and you can't fuzzy guard the low or mid option. H+K can also punish holds out of stun, meaning that you can watch a high or mid hold, wait, then get a Counter hit by striking with H+k. PPK will grant you all of the perks of the move as well. But H+K is all that is needed.
4H+K is the second move that grants her the ability to bypass the stun game, on NH hit it causes a sit down stun that can be SE'd. On Counter to Hi Counter it causes an unholdable sit down stun that guarantee her a launcher (3H+K) this move is safe, only grapplers can punish it and that's if they step up quick to do it because on block it pushes. So when players try to low hold from Kasumi's H+K, 4H+K will give you an unholdable stun as well.
H+K is the better unholdable stun but they both allow Kasumi to bypass the stun game when worked properly. So factoring in her usual play style; playing in the stun game to bait holds, Kasumi can now bypass that with unholdable stuns followed by damage as low as 71 pts of damage to as high as 98 pts of damage.
Low or mid tier characters cannot not do this but there's more.
As many of you should know, Kasumi has Untechables. They leave her at +9 to +14. The ones they will be worked the most are the ones that leave her at +9 or 10. The only problem with her untechables is that they are not as fluent as Helena's. you have to sacrifice damage for Kasumi's untechables and the need to setup them up is not worth doing all the time, unlike Helena. However, Kasumi does have a nasty force tech game, the frame advantage from it is ridiculous for a character at her speed level.
All of the characters have something crazy next to wall. Kasumi's wall game is one of the best wall games in doa5. She can re-launch any character and juggle them right back into wall ( I invented this shit FYI). No matter hit that You get slammed into the wall the damage output from the juggles is fairly high. My bad for not having the exact numbers on this. If you were watching me on stream I am sure you saw it.
Almost forgot, Kasumi now has a punish throw. Which is a problem for players that disrespected her by finishing things in doa4. Knowing she couldn't do anything about it. Now she can snatch up players for playing reckless. It is a typical punish throw but it helps defend herself better than before.
Kasumi in a ceiling area shoots up the tier list (top tier) for as long as she is in it. She has 3 extremely viable ways of putting you in the ceiling. 236T, 1T and 46H, all of these moves are a major part of her game play and you will be caught in at least 2 of them. Once you are caught by any of them Kasumi is taking half life (150 pts of damage).
Kasumi's damage output is high, to get to her damage she needs to get counter or hi counter hits to start with. I cant give exact numbers on this because combos/juggles vary after the counter or hi counter hit to initate the damage. Getting counter or hi counter hits would be difficult for her if was slow. By her being as fast as she is Kasumi will get the hit statues she needs to deal her damage. So Kasumi relying on Counter or Hi Counter hit to deal damage is not a problem for her in the slightest bit. Hi counter throws will cost you a quarter life (100 pts of dmg). Her advanced mid kick and low kick hold will cost you at least a quarter life.
Kasumi's parries now grant her guaranteed damage. Moves that are safe or pokes her parries will not give her anything. But she will eliminate 2 options with a parry. Moves that are unsafe or strings that are continued and she parries Kasumi will get a free knock down or she can launch. This does depend on what she parries but again she eliminates 2 options with one move and she gets guaranteed damage from it.
I am watching top 8 at NEC right now. So I will leave info to unknowing players of what Kasumi really is. I will continue this later because there is more if this isn't enough to make her high tier.