First of all, thank you. I have another question. Are there different species (ı mean elf or wolf girls like that) ? Can we only tame these humans? Or are there special characters?
There are bog-standard natives, old natives, DLC natives, large (read: SWOLE) natives, small natives and underground people. All of these are befriendable/tameable (female only for underground).
Old natives can be rejuvenated to become Big Brother/Big Sister natives. Underground women can give birth to underground DLC units. Underground women can be upgraded into Sadako by pulling a Ringu on them.
Mummies are also tameable. Guess it counts as a alternative "monster girl" species of sorts?
You can also create androids using dead body parts.
Other than that... you need to befriend special unique NPCs for alternate species. There's a mermaid, a giantess, a fairy (DLC only), an undead spirit/reaper and an unique android (looks mostly human though, unlike the androids you make). You get these by completing side quests instead of the usual capture and taming process. Oh and there's also an ent (tree lady) but you need to finish the main quest for her.
Artwork has been done for generic mermaids (and mermen), but so far no news on them getting implemented yet. There are requests from other people for more "monster girl" species, but IIRC the programmer is reluctant to implement too many of them.
There is a wide variety of tameable animals though.