Due to your eternal fight for honor, you have obtained the knowledge about creatures of darkness such as Undead and Demons. This not only gives you an advantage in combat against them, but also allows you to use this very knowledge to enhance your own abilities.
As a Bonus Action, you can speak a Command Word to coat your weapon in a hybrid of Divine and Unholy energy, making it reach a perfect equilibrium. For the next minute, this weapon deals an additional 1d4 + Your Proficiency Bonus Radiant Damage and shines Bright Light in a 20ft Radius centered on yourself.
On top of that, whenever you hit a creature with a Melee Attack it must succeed on a Wisdom Saving Throw for which the DC is 8 + Your Dexterity or Strength + Your Proficiency Bonus. If the creature fails, it can only attack you until the End of its next turn.
Additionally, whenever you make an Attack Roll against a Undead or Fiend, you have Advantage on the Roll. Once this effect ends, you cannot use it again until you finish a Long Rest.