Death likes to start off in one of two ways. His cloak is dark, and he is very resistant to physical damage. So blast him with Holy Lightning when he is right above you. From time to time, he likes Demonize himself, and his cloak turns white/gray. He also gets a red aura, and his physical attacks deal more damage. When he is Demonic(white/red), he is resistant to Magic(all Magic damage dealt to him is reduced to 1), but he takes more damage from physical attacks. When he casts his cage in his Demonic form, switch your Dual Crush to 1000 Blades. You should probably cast it from a safe distance in one of the entrances. Each blade deals 21 damage, and it adds up pretty quickly. He has 4444 HP. I think I was around level 27 at the time, but you should probably level up to 30~32.
1. He creates a cage, and spins his scythe inside the cage. You won't take damage if you're outside the cage. Once the cage takes enough damage from either you or his scythe, it will break and the scythe will spin off towards the left or right. This is when you cast Holy Lightning right underneath him. It deals 31 damage over and over very quickly.
2. He creates mini scythes, just like in Aria/Dawn of Sorrow. His body type is very similar to his Symphony of the Night form, but anyway... There are about three or four in each screen. If you go under Death, he will swing down on you. Or, he will turn around, and do a backswing for 42 damage. He does this about three times. Then he will do his cage attack.

After he has performed his cage attack, he will open up all four of his cage arms. They will attempt to grab you starting from the top left hole, clockwise eight times. If Death fails to grab you, he will repeat the process. If he fails the second time, he will only do it for the third time and then go back to his Attack#1 or Attack#2. If he does catch, you're pretty much screwed. He takes his time while you're held by the cage arms, and then he goes off screen to smack you for 264 damage.

After a few attacks, he likes to turn white, and then back again.
Death is a hard boss, but I hope you have fun fighting him. I hope this strategy helps.

I found an easy way to defeat death.
What i did was that when he did his cage thing i used charolette to use dark rift under death(charge it all the way so that it is stronger) and start hitting him with both characters while dodging his sythe. make sure that you stay uder the dark rift so that death takes damage.When death turns white just start attacking him until he turns black again just repeat the dark rift. When death does the thing where the cage hands grab you its faster to just get caught and let your partner get you loose.Your partner will attack the hands while death takes his sweet ass time prparing his super strong attack(your partner will set you free before death is done preparing his attack)
Thats how i did it and it worked

I'm just too lazy for all that.

I used the WIND/ERIC glitch, got me a ton of cash, bought all the potions/high potions & tonics/high tonics and the powered milks! lol

And waited him out!

haha better way:
wait till he does the scythe bouncing on cacage thingy
then use greatest five and break the cage BEFORE the scythe TOUCHES it
he will float around stupidly and his scythe is frozen OMG OMG OMG

Too bad you most likely wont have that spell before death.

Unless you are doing a re-run.