You have Celestial Blood running through your veins even if you don’t know about it yourself. At some point in your live it awakened and the results are:

• You know the Find Familiar Ritual Spell. The Familiar can’t be a Fiend.
• Your existence has a calming effect on Animals around you, giving you a natural expertise in Animal Handling.
• You gain a Celestial Trait that manifests on your body depending on what specific type of Celestial Blood awakened inside of you. You can determine it by your back-story or a 1d4 dice roll. You can also let your DM decide on a trait or even the point of time the trait emerges for the first time. Depending on the Trait you gain a Special type of Bonus Damage added to your Attacks. This Bonus Damage can’t trigger on the same target again until 1 Minute (10 Rounds) passed or until you gain advantage against the target which instantly resets the cool down time! But it can only trigger once per turn. It deals 1d4 damage, increasing to 1d6 at 5th, 1d8 at 10th, 1d10 at 15th, 1d12 at 20th level.
• Optionally, the DM can also decide to have this Trait give an additional effect at the same or a later time if it make sense to him. For example a resistance corresponding to the Archon Traits skin color or the Angel Traits Tiny wings growing over time giving you flight etc.