How write sympathetic "monster" character while keeping them as threat

So in my plot the main cast consist of monsters (either paranormal and fantasy)

• The MLI, Kage and his twin sister Hikari niku (a flesh eating, basically a zombie with a brain and isn't rotting and stuff)
•The FLI, Minato is a human, a really strong human
•The MC, Asumi is… something, he's related to a god, who had a bunch of kids with a bunch of species, who all died beside the half-human
• The rival consist of:

Eri, Asumi's cousin who is a nephium who can control gold
Collin, Asumi's classmate, who is a fae(based loosely off the Fair Folk who controls dreams
Mikoto an oni who feeds off emotions
Hanaki a vampire who can shift forms (a gargoylic form and a human)
Emiko a witch, a very frail and weak witch at that
Unzari, an incubus, working with his human father
And Hikari, she's strong for a Niku that's all I say

You see most of the afmentioned characters are humanoid looking, has a tragic™ background that explains _{not justify} their more vicious behaviors, I want them to be sympathetic but I don't want accusations of "wussyifying" a species, especially with Kage who's typically despairing and Unzari because despite the fact that he's a literal demon, is selfless and self loathing to a fault to the point of allowing himself to be toyed with by his douchebag borderline pedo of a dad, and the majority of the characters were normal people who are normally kind, peaceful and gentle before being forced in the game

A lot of movies or whatever will have the monster be really sweet and cinnamon bunny around a person they trust, then suddenly completely change and be super defensive and stuff if that person (who they trust) is under attack.
I don't know if that helps you because it's pretty general, but it's all I can think of.

Also, you probably won't like this, but Asumi is basically just MCU Peter Quill (because that is exactly what Ego did) (or even if he's not that god's son, the god did what Ego did)

'Monsters' don't have to be born different, as humans can resemble them just by their actions.
In fact I'd go as far as to say a monster isn't born as such, but come from the conflict between them and another.
In our minds we may be caring and sympathetic towards animals, but on a species level, most animals fear us due to our history of behaviour.
If you play with the situations that make up the conflict, you can turn the tables on relationships.

Primarily, you need the audience to relate to them somehow, focus on the similarities rather than the differences.
You seem to have a 'family' of monsters, perhaps giving them opportunities to demonstrate 'positive' traits that relate to that dynamic, even allowing them to have 'codes of conduct' that give them a morality of sorts.
Having your monsters demonstrate 'good' behavior towards those that aren't threats or prey themselves can open such opportunities.
Perhaps a character is thrust into their sphere of influence without being an immediate opponent?
Perhaps they have a relationship where they are tolerated due to circumstances, environment or happenstance?
Maybe one of the rivals is a long lost progeny of Asumi, either known or unknown? (perhaps instinctively by both parties?)

Personally, my most productive way to develop characters is to brainstorm personalities from taking them on adventures into backstorytelling.
I don't believe in Tarot cards for divining the future, but I taught myself the basics to allow myself to learn about my NPCs. I bought a card set that had the meanings written on them (including the reverse or 'negative') and 'read the fortune' of them.
There are different ways to do it (called spreads) - I tend to use the Celtic cross just cos its the most common.

It is intended to shed light on many aspects of your characters life, and the cards drawn are compared to the meaning of the position in the spread.
-The meaning of the first card represents their current state of being.
-The second denotes that which opposes or influences them
etc etc till you put together a picture of meaning of their past, future, obstacles, achievements etc
Its a bit like story dice but with more variations.
Then you just weave it all into a narrative, backstories within a bigger tale

After youve giving them a full range of personality, there should be opportunities you can exploit in your story telling.

Even normal playing cards can be used to spice up NPCs, as I'm currently working on a system where you can find the emotions for your characters utilising Plutchik's 'wheel of emotion' from only 4 ranges of mood!