There are numerous good places to level up. However, one of the best at a fairly early stage of the game is the part before the stairs leading up to Hideyoshi (the first time), any time you are there. (there is a save point next to the stairs leading upwards)

When there, allow the enemies to attack the other character who is invulnerable whilst blocking. Wait for one to block, when this happens, charge him, kick his block, and tap square as quickly as possible, many times. This will cause a chain critical. Once this has been done, face the camera in the direction you wish the creatures to appear, and they will do so obediently, allowing you to destroy them again.

Similarly you could just use magic, but there is no guarantee of replenishing it once it has been utilised.

The best place to level up in the game is on the final charge against Hideyoshi, charging the castle, there is a room when all the "zombies" appear. Here, you can use magic aplenty, since it pretty much replenishes once it has been used due to the multitude of souls. Continuously chain critical the creatures and you get much soulage for power ups. In the next screen there is a save point directly to the right, down the turning.

*take note, the criticals and chain criticals will only work providing you have levelled up chain to a sufficient level, as well as critical, otherwise it will not be as effective. Max level will suffice*

When your low on health just switch characters and press the down D oad button to make your soki heal to half health. Then do the same for your other person.

When you're at a hideout, talk to Minikichi ( I think it is ) and do "Revisit".

Pick any stage and head back there. Kill things and absorb souls, then find any Enchanted
Mirror and do "Return to Hideout". Then, revisit the stage you were just at. This is a great way to get souls and upgrade things fast.

To beat him when he tries to make the star absorb the essence from the star and then when he throws it at you deflect it.

He will be stunned then destory the spheres surronding the field then he will come down then use cooperation attack or if you run out of magic.

Just attack him but to be prepared come with oni potions and drive potions and make sure your oni point gauge is full at the beginnig of the battle it will go much smoother.

This is how to beat him when he first tries to make the star adsorb it and when you're done adorbing it he will throw it at you when he does deflect it then he will be stunned destory the spheres and he will come down thats when you use the coop attack and when you run out of MP just attack him and repeat

First of all his attacks are deadly so try to aviod by staying in the middle of the bursting lights by moving around and so forth, but to beat him you have to absorb the essence from the star.

Deflect the star, and then when that happens he'll get stunned attack by the spheres.

He'll fall when he's down fully down use co-op attack or if you run out of magic just attack, and then repeat.