Things will become complicated as the days continue to pass. Genkai is not only a master at mentoring, but she's also a master at keeping an emotional distance. She loved Yusuke like he was her own child, but rarely ever allowed him to see that until she died. Kurama, in the same position, probably couldn't hide himself behind a mentor persona without destroying the relationship they already have together. He'd rather be a mediocre mentor who keeps a friend than a great mentor who lost a friend. We gon' see~

Assuming whoever is writing our individual stories would let us be so lucky.