so the reason he got into Hikaru is to fulfill Hikaru's dad's wish?

I don't remember really well what Hikaru's wish was (taking care of Yoshiki, not leaving him alone or smth) but it was bc of that that 'Hikaru' got into Hikaru. Hikaru's dad's wish was just for 'Hikaru' to be free of his confinement, and then when he was free and roaming I think he found Hikaru when he was dying.