Guys, I know it may be frustrating, even I thought this matchup was all in Mitsuru's hands until a friend of mine (also a REALLY good Mitsuru) gave some advice. Chie can 2A punish just about everything Mitsuru does. What sucks about this matchup is that you are forced to play Chie a different way than you might be used to. You all of a sudden have to take it slow and be patient. But if you block patiently you really can short dash 2A her out of everything. Sweep 5DD is not safe but if you feel that they are gonna do 2B (since it is like her only option out) that move has hella recovery so as long as you stay grounded you should be able to punish it safely. Believe me, Chie can really get under Mitsuru's skin.
What you SHOULDN'T do is try to challenge her space. Don't try to dash 5C, don't try to challenge her air to air, don't black spot randomly and don't jump towards her recklessly. Mitsuru can literally 5A or j.5A all of those and you find yourself without a persona in seconds. Also, Chie's Furious Action isn't good against Mitsuru because Mitsuru is all about frame traps, 9 tims outta 10 you are gonna get fataled if you try to counter out of her pressure. What you should be abusing is Chie's j.5C's ability to delay your descent upon jumping. Like Air dash then j.5C in the middle of the dash to alter your landing so Mitsuru won't be able to 2B you to hell.