Here is the full list of all 27 Dark Hero Party achievements.
Watch the opening.
Watch the ending.
Defeat 5 enemies.
Defeat 20 enemies.
Defeat 50 enemies.
Defeat 100 enemies.
Complete the 1st chapter.
Complete the 2nd chapter.
Complete the 3rd chapter.
Complete the 4th chapter.
Complete the 5th chapter.
Complete the 6th chapter.
Complete the 7th chapter.
Complete the 8th chapter.
Complete the 9th chapter.
Complete the 10th chapter.
Watch Lotia's first scene.
Watch Lotia's final scene.
Watch Tori's first scene.
Watch Tori's final scene.
Watch Aina's first scene.
Watch Aina's final scene.
Watch Krimina's first scene.
Watch Krimina's final scene.
Defeat the boss in Amari's Cave.
Defeat the boss in Discene Path.
Defeat the boss in Mokene Lakeshore.