I mean I'm no expert I just gave my quick thoughts after playing him a few times. It probably depends a lot on the mu too and I've only played two games vs Miska and one game vs Reese. But here is some general stuff, maybe some of it will be useful to you.
He is a build up character since he wants cards in his discard and he wants two copies of the same card either in his hand or discard. For this reason the Change Cards action (not sure why this doesn't have a more thematic name. Drawing a card gets the title of Prepare but discarding cards to draw cards gets the title of change cards) probably has more value for Kaden then it does for most of the cast. This can let you get several cards in the discard and potentially draw into a second copy of another card you still have in your hand.
Having cards in the discard is very important for Kaden because of all his discard manipulation abilities. He's got Double Charge Executioner, Recall, Dark Tide Summon, and Silence (seems poorly named, lol). So you'll need to start getting cards in the discard one way or the other so he can start making use of these abilities. Silence or Dark Tide Summon into Double Charge Executioner bringing back Dark Tide Summon is a personal favorite.
Several of Kaden's Specials are very mu/situation dependent so knowing when those cards are good seems important. I think His situational attacks are: Havoc Call, Chain Strike, and Calamity Bell. Havoc Call and Chain Strike are really good vs Miska with Calamity Bell being pretty bad. Against Reese Havoc Call and Chain Strike are pretty situational while Calamity Bell is strong. These three attacks all have really good boosts and Perfect Evolution and Recall are both good at setting up EX attacks.
Fusion Bane and Double Charge Executioner are great attacks and help him further set up his offense but at speed 1 they have a lot of counters. So knowing when they are safe to play is important. There are even quite a few normal attacks that will beat these moves but putting the opponent in the right position can take away some of these options.
One important point about Double Charge Executioner and Fusion Bane is both of their card gaining effects happen as an after effect. So even it they don't hit as long as they weren't stunned you'll be getting some cards.
So the basic game plan is get cards in discard then use his abilities to get the cards he needs back to set up his EX attacks. The downside to this is the opponent knows what cards are pulled out of the discard so they'll have a pretty good idea of the EX attacks you're cable of. You can use this to your advantage or you can just play defensively so the opponent can never be certain you'll play an EX attack.
That's a lot of rambling. Hopefully something in there is helpful and makes sense. Try using the Change Cards action to jump start your game if you're having trouble with that. Or just play a normal game and then use your Gauge for EX mode early to get cards in the discard that way or use EX Rising Host over and over to get your Gauge in the discard. Then Save the Insurmountable boost of the late game.
How have you been playing Kaden and who have you been playing him against? I'm curious what your experiences with him have been.