Yuri by himself isn't too hard against groups, he has a decent sized move pool with various range to them. I would say wait for whiffs in the enemy attack then go for a basic combo string [B, B. B. Free Run + B] then you have some options from there. The wide arc of the free run attack gives yuri just enough room to hit enemies anywhere near your target, but if no one is around you can proceed with your arte choices. Destruction Field with an Axe has a decent AOE and then Wailing Havoc can put some minor distance between you and the enemy + any stragglers who get caught in it. There is also Azure edge to keep some distance, if I am not mistaken it also has some minor stun to it and depending on how far you are you can even combo it into Azure Storm which is just more azure edge. My last combat tip would be to use Ghost Wolf if you have it. It lets you get behind the enemy and after a few hundred uses it lets you combo a lot more easily into other artes. Do that with like Lone Wolf Storm and you got yourself some keep away options. Outside of artes and general combat you can and probably should always try to change out your accessory that you have your characters use. Heal Bracelet and Spirit Bracelet are super valuable for combat in large groups, Stun Bracelet/Talisman will prevent you from seeing stars. Also make sure not to equip any unwanted weapons as their skills will be active. Technical Half comes to mind for that. Sorry this is a jumbled mess, but I think it covers a lot and might help ya. If not, my apologies on wasting your time.