uh first off im a little confused but i am guessing you mean start a relationship with them? because if that is what you mean yes you can have a relationship with anyone that has a relationship bar which can be found the menu thingy on the bottom of the screen.
second off, no the character is intentionally anonymous so we can imagine the character instead of having a specific base, which also makes us need to worry less about update times sometimes since the MC doesn't have a "set" design he can't have CGs meaning scenes with the MC only require the text and other person/persons to be present on screen.
also, on the change your species thing, a lot of people want it, be it a way to start off a werewolf or Lizardfolk or eventually becomes one via idk a bite (Werewolves) or like a ritual (Lizardfolk) maybe even a rite of passage (Orcs?) but it is currently not implemented, and I do not know or believe Hyao really plans on adding it in. I do not know all his choices or what he's planning so in all honesty it is a very large possibility if enough people want it. unless someone asked it and a while back, he said specifically no and I missed that, which would be the only confirmable way for us to know if Hyao plans or not to add them in.