I have fought NorCal's beastly Setsuka (Shenrei) in offline casuals a good number of times and here are my thoughts on the match up of Cass vs Setsuka.
General Observations:
1) Setsuka is faster than Cass. Do not try and beat her out by sheer speed.
2) Setsuka can be played very safely. Take what few punishment opportunities Setsuka gives you.
3) Setsuka similarily suffers from a lack of lows and has a shorter throw range than Cass. In other words, do not duck unless given a solid reason to do so, especially at range.
4) Setsuka similiarily suffers from a poor oki game and has few ways to force opponents to get off the ground and into her tech traps. In other words, do not always immediately get up off the ground once Setsuka knocks you down.
5) Setsuka's average damage is very high; both off of her combos and her throws. You are generally only allowed 3 to 5 mistakes before it will cost you the round.
6) Setsuka's SG game is respectable. She does not need to greatly go out of her way to break your gauge and can realistically break it once your SG is flashing red.
Basic vs Setsuka Strategy:
1) Do not duck unless absolutely forced to. Respect Silvery Moon (Setsuka's B+K series). Ducking is a 1/3 lifebar mistake.
2) Throw break B by default. Setsuka's command throw also a B throw. There is no reason to respect her A throw unless she is in position for a reverse RO attempt or unless they can demonstrate that they can reliably hit the guaranteed combo that follows the A throw.
3) Setsuka has two options for reverse RO: her A+G throw and the B+K series. When Setsuka's back is towards the ring, throw break A and do not duck.
4) Pay attention when you use moves that force crouch or when Setsuka enters a crouch state through her attacks. Respect the Umbrella. Even without the threat of Umbrella, Setsuka's While Rising game is very strong. Additionally, Setsuka retains full access to all of her 8 Way Run moves from the crouch position via her Wave Dash.
5) Do not be overly aggressive with High's. Setsuka has good moves that have excellent TC properties (such as 33B, 4A, and Umbrella).
6) Take your punishment opportunities. Practically every blocked Setsuka Low can be punished by at least FC 236B. Umbrella is majorly unsafe for Setsuka if blocked. If Setsuka cannot reliably hit her JF's, then those moves become unsafe.
7) Generally step to Setsuka's right (which is Cass' left). Cass is one of the few characters who can step Umbrella - so make sure you are stepping the correct relative direction.
8) Watch your ring positioning. Many of Setsuka's combos can RO from a fair distance when your back is near the edges.
9) Again, for emphasis, do not randomly duck. Other than 2K, Setsuka's only useable lows are all blockable on reaction offline (11A, 1A:A, and 2A+B).
Miscellaneous vs Setsuka Information:
1) Setsuka only has one "frame trapping" type of move on block, which is her 4K. Even then, her 4K on block is actually +0; so you are both at neutral. Learn to recognize it so you do not eat CH's afterwards.
2) Setsuka's only real Guard Break move is 66A+B. Bear in mind that blocking this move actually leaves Setsuka at a minor disadvantage. Do not let her get away with it and go initiate your offense.
3) Learn the difference in animation and audibles between 2A+B and B+K. Both look similar at start-up and neither are fun to be hit by.
4) Re-GI is risky since Setsuka can always try to B+K after she GI's. Learn to shake the stun on NH 4K.
5) Getting Setsuka to block WSK does not leave you with many offensive options. Umbrella will beat out almost anything you do even though you have a sliver of advantage.
6) Do not get predictable with 2A. Having Setsuka TJ it with an 8K or A+KB for a knockdown sucks.
7) Do not get recklessly predictable with BB. Having Setsuka step BB and whiff punish with B+K for 1/3 of your lifebar really sucks.
8) Be patient with your offense. Many of Setsuka's pokes and main combo starters are safe. You do not want to get baited into eating a CH 4A. Losing 1/3 to almost 1/2 of your lifebar for attacking while at frame advantage using a non-TC move really really sucks.
9) It is more visually advantageous for Setsuka to be on the 1P side. Her back side helps cover a lot of her hand movements and makes 1A
A that much harder to see.
Setsuka Move-Specific Notes (not a complete list):
AA
Her AA is faster than Cass' at i12. It allows her to easily punish some moves that few otherwise could, such as Cass' 66K or WSA. Safe.
3A
Slow anti-step with good TC properties. Puts Setsuka into crouch for Umbrella mind games similar to post-2A or post-2K. Safe.
1A
A
Setsuka's trademark low is the only low she needs. This move is one of her primary tools outside of throws to try and get people to duck. People do not want to duck on Setsuka, but at some point they are going to have to attempt to block this or they will become very good friends with the floor. The 3rd hit is an on-hit only JF with GB animation for flashiness. This is a Low-Mid natural combo string and is very unsafe on block.
4A
Backsteps and has good TC properties. NH will force opponents into a BT state. CH leads into a hugely damaging combo. Safe. You do NOT want to be hit by CH 4A. The attack is a High, so use forward advancing TC moves that hit Mid such as 66A or 66K.
FC 3aB / FC 3a:B / 2143aB / 2143a:B (aka Umbrella)
Setsuka's trademark punisher is fully accessible whether she is standing or crouched. Very fast attack that can be used out of slight disadvantage with good forward movement and TC properties. Normal Umbrella is i13. JF Umbrella is i12 with a larger hitbox. Can be stepped to Setsuka's right by a limited number of characters. Very unsafe on block.
bA
Fast ranged anti-step. Has good TC properties and forward movement. Unsafe when she uses it at close range, but completely safe when used at max range due to block pushback.
1B:B
One of her bread and butter combo starters with a decent range. One of her primary tools to hit grounded. Can be used as a shakeable tech trap. JF version is safe. Risky to punish even if they occasionally fail the JF.
WSB
Fast combo starter with some TC properties. Safe.
FC K
Be advised her FC K has much more reach than her 2K. Minorly unsafe.
4K
Her lone frame trap. Not the best trap since it leaves you neutral on block. If you get caught by this move, the stun is shakeable.
A+B (aka Mirror Blade)
Her only useful aGI. aGI's all Mids that are not "stabby" or "body" attacks. It means Cass can try using more 66K or 66A+B, but be advised that Setsuka is one of the few characters that can punish these on block.
2A+B
Slow combo starter. Early animation looks similar to B+K. One of her tools to hit grounded. Low attack that stuns on hit and she recovers standing. Minorly unsafe. Cass is one of the few characters who has a good punisher for blocking this.
B+K Series (aka Silvery Moon / Sakura Fury)
Another Setsuka trademark and the number one reason not to duck against Setsuka. Can lead to reverse RO. Forces crouch on block. Minorly unsafe. Cass is one of the few characters who has a good punisher for blocking this.
11A
Slow Low with good TC properties that gives advantage on NH or is a combo starter on CH. Cannot hit grounded but can be used as a tech trap. Unsafe.
33B
Her bread and butter combo starter. It is fast, has good forward movement, and TC's. Has moderate tracking to one side and can partially tech trap. One of her primary tools to hit grounded. Safe. She can bait her A+B aGI very well after this move gets blocked against Cass.
66A+B
Her GB. Can hit grounded. She is at a small disadvantage on block despite the fact that it is her GB.
A+KA
Ranged anti-step that TJ's. Safe.
