Kouichi

Kouichi spent the first half of the series under the command of Cherubimon, who enslaved him using the corrupted Spirits of Darkness. When confronting him about it, Kouichi unlocks the true power of darkness, transforming the spirits into their true form. Now instead of the eldritch-looking Duskmon, he turns into the knightly Loweemon, who while wears black armor and uses darkess-based attacks, is firmly a heroic warrior.

Example of:
Dark Is Not Evil