I keep making up adventure stories and then never doing anything with them sob
Anyway these two are the main characters in an epic adventure! The centaurs home was raided by foreign soldiers (as it always is) so she runs to get help from the deer king, only he's a butt and turns her out on her rear. A single scout comes after her and says she was sent by the deer king as a 'token of good faith' which just infuriates the centaur more! The deer girl says not to worry, there are other lands we can get help from! So they set out and find out the problem is bigger than they thought (as it always is!)
The ~~secret plot twist~~ to their developing relationship is that the deer girl is in fact, the deer kings daughter and only remaining child. She was sickly when young and her twin was kidnapped and never seen again so her father cloistered her away and forbade her to learn to fight (in her culture ALL royalty fight, as they get preyed on by other, bigger predators).
So she said 'fuck da police' and learnt to fight anyway and is terrifying with a spear. She's actually the most bloodthirsty of the two and the centaur is constantly having to remind her that diplomacy will, in fact, work in most situations where stabbing will not.
The deer king is both horrified and proud as heck when his daughter turns back up with an army behind her, demanding they join the cause.

Centaur is based on a Belgain draft horse (god those things are so beautiful they are the perfect horse) while the deer girl is based on a Chital deer! There are other deer people in the storyline, like the hog deer of the coast and the sambar of the wild forests, but really only the sambar are notable in the story.