Johnny_Samhain
It’s a vague description, so I can’t be too specific. My biggest question is, what is the plot? MC finds Neko, who is a familiar no one else can see, from the god of love and war. now what?
Is there a war about to happen? Are they paving the way for Nekos to eventually appear to humans? Is another god going to attack them? There has to be some sort of conflict to resolve. It doesn’t have to be action based. Maybe the MC is incapable of finding love and Neko is his soulmate, but he really wants to marry a human at the start. Up to you.
Some more general thoughts:
Neko the Neko isn’t very original. What happens if they meet another neko? Call her Neko 2? It’s not terrible to keep her name Neko, especially if she is the only Neko in the story, but consider another name or nickname.
Make sure your MC has a plan. Both his and Nekos personality should be planned and consistent. Their interactions should be endearing to make this work. For example, maybe the MC is a clean freak. Cats are pretty messy. Often it seems like they do it on purpose. So maybe Neko and MC constantly fight because Neko makes a mess and he has to clean it up.
Their relationship will have to develop. Remember that when the MC first finds her, it is a surprise. His reaction should match that. There should be some tension and mistrust at the beginning that slowly disappears over time. I would watch anime or read stories with relationships like this. The Rising of The Shield Hero comes to mind. The MC buys a Demi-human slave early in the story after being tricked by his original partner. the MC doesn’t trust her because of what happened to him in his past. She doesn’t trust him because her last owner was cruel. It takes awhile before they trust each other and build their relationship up.
These points aren’t too specific. Depending on your plot they might become irrelevant. I just caution you to think about these things ahead of time to avoid something like this:
“Who are you?” MC asks the cat-girl laying in his bed.
“I’m Neko the Neko! Call me Neko, meow!” she says back like a cat.
“I love you!” The MC says.
“Meow! Purrrrr.”
If this is the first conversation in your story, something is wrong.