You can level up hit points, power and magic by replaying older levels repeatedly if you are having problems.

ACHIEVEMENT - HOW TO UNLOCK
Moon Traveller (25 points) - Visit all areas in all stages.
Chain Kill Master (15 points) - Achieve a Chain Kill of 100 or more.
Overprotective (10 points) - Save your companions 10 times in a single game.
Act. 1 CLEAR (5 points) - Clear Stages 1–4.
Act. 2 CLEAR (10 points) - Clear Stages 5–8.
Act. 3 CLEAR (15 points) - Clear Stages 9–12.
3P MC Practise (10 points) - Use 10 different 3P MC techniques.
4P MC Training (10 points) - Use 10 different 4P MC techniques.
Battle Master (20 points) - Defeat 10,000 enemies.
Level Maniac (50 points) - Raise the average level of all characters to level 50.
MC Collector (20 points) - Collect 50 MC techniques.
2P MC Drill (10 points) - Use 10 different 2P MC techniques.