The story could have easily gone the "Fuck this world I'm getting revenge" route but I'm glad it didn't, yeah they are basically human leeches but it's not like they are strictly evil.
Also do they literally practice by fighting ,or is just an euphemism for sex, or maybe both at the same time lol? (btw if she's in the innate realm that means she can grow an innate dick and fuck the MC right? I hope that's canon lol)