The first step in any Mitsuru match is to make him/her respect your 2A. It gives you enough upper body invincibility to completely low-profile Mitsuru’s 5A and Coup Droit, 2 of her best poking tools. Practice doing dash 2As (input a dash, then instead of returning the stick to neutral, slide it from forward to down/forward and hit A) and confirming those into knockdown combos.
You also need to make them respect your 5DD oki setup. ALWAYS hold back to block for a brief moment before going in for your mixup, just in case she tries to wake-up DP out of it, and if she did, punish her hard. Practice punishing her with dash 5B BEFORE she touches the ground after a DP; this completely removes the risk of eating a Bufudyne upon her landing as so many Mitsurus are fond of doing.
Mitsuru also has a unique answer to the oki setup: wakeup 2B. It has some funky invincibility properties that allows her to hit your persona and get out of your setup clean. The 2B will also catch you if you were jumping towards her. If the Mitsuru starts doing this, you need to adjust the timing of your 5DD to be a bit later than usual. If timed properly 5DD will be a true meaty attack and 2B is no longer a viable escape option for her. But you do this at the cost of a less effective mix-up: now your persona will push Mitsuru farther away, not giving you enough time to get to the other side of her. This makes your mixup is one-dimensional, but still effective. Practice IAD’ing after your delayed 5DD and going for any combination of highs and lows.
For the most part, you should cool it on using your own DP in this match. Mitsuru can hit you from safe ranges where your follow-up kicks won’t hit her even if your DP is triggered. And Mitsurus LOVE to 4B Fatal Counter people when their opponent thinks they have a window to push their own buttons. If she has you blocking, just be patient and react. You’ll get hit by the occasional j.B overhead while you’re blocking, but she can only convert this into a combo by spending 50 meter to OMC it. So try not to panic if you keep getting hit by j.B.
There’s more but I’m tired, lol. Hopefully these are some good starting points.
OH. And Mitsuru’s 5AAB is not safe before the B if she holds down B to delay it. This is the only part of her pressure I feel comfortable using my DP to get out of.