It's a fun and difficult game with an interesting take on Ikaruga's gameplay. The switching mechanic was fun during the stage, where you could hit most of the enemies with Iku first and then finishing them off with Tenshi (the exception being the ghosts with red gloves, who need a T-I-T combo). However, it's a bit lackluster during the boss fight, where the character that you'll be using most of the time will be Iku, since Tenshi has such a low range and damage output against Miko in comparison.
The best implementation of this mechanic in the boss fight was the 3rd spell, where a curtain of either blue or red bullets approach you from behind while ghosts swarm the screen, here you can paralyze the enemies with Iku, switch to Tenshi to kill them, avoid the bullets and even damage Miko with Tenshi's sword.
It was a nice experience overall.