Basically, a Naga is a human with a large snake tail instead of legs. They also usually have some scales, pointed ears, long/forked tongues, and fangs.

Either your Oc or crush can be the Naga.

There are a few characteristics below to help you design your Oc/Crush as a Naga for this au.

Lamia subspecies: Generally nicer, they're nonvenomous and live in tribes.

Echidna subspecies: This subspecies usually has claws, and scales covering their arms. Sometimes they're venomous, they usually have jeweled eyes with narrow pupils.

Melusine subspecies: They have two pairs of dragon or feathered wings on their back, slit pupils, jeweled eyes, scales on their cheeks and necks, and fangs. They can also have horns.

Eyes:
-Jeweled.
-Normal.
-Round pupils.
-Slit pupils.
-Usually a bright color.
-Almond shaped, sharp.

Tongues:
-Normal.
-Long.
-Pointed at the end.
-Slit snake tongue.

Teeth:
-Fangs for their upper canines.
-Shorter fangs for the lower canines.
-Sharp teeth.
-Only small fangs, pointed backwards.
-Catlike fangs and sharp teeth.
-Large fangs.
-Long fangs.
-Smaller fangs.

Scales:
-On the cheeks.
-In stripes beneath the eyes.
-Patchy on the neck and collarbone.
-Patchy on the shoulders.
-Patches all over the body.
-Covering the arms.
-Covering the hands.

Colors:
-Must match the character's aesthetic.
-Can be shiny, or dull.
-Diamond shaped.
-Rounded.
-Sharp, like sharkskin.

Venom effects:
-Paralysis
-Unconsciousness
-Nausea
-Weakness in limbs
-Chills
-Death, depending on the amounts.

Weaknesses:
-Cold.
-Extremely hot temperatures making them sluggish.
-Chilly temperatures and wind making them lethergic.

Habitat:
-Snowy. (Harsher/soft colors, still shiny, but darker. Cold colors.)
-Desert. (Light colors, warm colors, dull.)
-Jungle. (Brightest and most colorful.)
-Forest. (Shiny colors, camouflaged.)

Traits:
-Possessive.
-Wanting affection.
-Controlling.
-Manipulative.
-Misunderstanding.
-Sweet.
-Soft.
-Cold.
-Distanced.
-Intelligent.

So you choose which qualities. 
For my Oc, these:

-Melusine subspecies. 
-Slit pupils and jeweled eyes.
- Loner
-Long tongue, pointed at the end.
-Catlike fangs, long for the upper canines.
-Scales on the neck and collarbone, a few patches on the shoulders and back, along with a few on each cheek.
-A cool, ashy purple/gray with tints of blue for the underscales of the tail, shiny iridescent black for the scale patches, and the outer scales for the tail are a blackish-purple. Diamond shaped.
-In small amounts, weakness in the limbs. In slightly larger amounts paralysis, and beyond that sickness and eventual death.
-Due to living in the normal areas, she can deal with the cold. However extremely hot temperatures make her lethargic, as she's not used to them.
-More possessive, and though intelligent, she doesn't understand humans.
-Bluish-jade feathered wings.
-Dark blackish-red rams horns.

Now, moving on to scenarios. Your Oc can either be a full-time Naga, always in that form, or they can have the ability to 'shed' their snakeskin(Which disintegrates into one scale on a chain that they wear around their neck)  and become human until ready to remove the necklace and become a Naga again. This Au set works for other Au scenarios and non-despair, as well as Ultimate Talent Development.

For one-liners:

Fluff starters;

1: "Don't leaveeeee...you're warm.."

2: "Let me braid your hair."

3: "Humans are so cute and fragile..."

4: "Aww, don't look so scared, love."

5: "I'll protect you from the outside world."

6: "Can we just cuddle for a bit.."

7: "Have I ever told you how truly beautiful you are? I don't say it enough.."

8: "Aww, stop moving! I'm not even crushing you!"

9: "You're so cute..I could just eat you up, you know that? Er, figure of speech, my dear. I don't intend to ACTUALLY eat you-"

10: "Stay with me...don't get up, or move, it's cold outside and you're warm.."

11: "Hey, don't squirm, it tickles! This is supposed to be relaxing!"

12: "Yes I was comfortable...up until you decided you could get up to go get a glass of water. Now I'm all cold again! Get back here and warm me up-"

Yandere/angst starters;

1: "You'll never leave."

2: "Don't try to escape...I'll only catch you again."

3: "I won't hurt you, I swear!"

4: "Don't look at me like that...I won't kill you..."

5: "You're so beautiful when you cry.."

6: "It's cute, your fear. But I won't hurt you, dear, I have other things planned."

7: "Don't try to run away again, I might have to hurt you next time."

8: "Don't be stupid, you're mine now. That means you'll never be able to leave me."

9: "No you can't leave, it's cold outside and then I'll have to suffer for it because you won't be comfortable anymore!"

10: "Tell me you love me, or I'll break you."

11: "You should be happy here. I love you. You have everything you could want-"

12: "No, you can't go back to your village. You're mine now, you're staying with me."

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Scenarios:

(Ight I'm going to write these later, first I want to publish the chapter because YES-)