While the game has a neat idea and is gorgeous to boot, there is a major problem.
If you die while getting struck by an attack, all the subsequent characters will have to just spawn and immediately die on the active hitbox of the attack. I would suggest letting the time pass while selecting the next character, since you have a time limit to kill the boss anyway.
Plus it would have been really cool if the different characters had like different powers or really unique weapons.
And finally, while I said the idea of the game is really neat, it's also quite heavily plagiarized from an existing game "Time Force Ultra". Which also has very similar graphics, down to the giant timer at the center of the screen.