Shoichi's battle with Obsidian did not end, neither side gave an inch and this kept on for sometime.
The boy kept exerting his strength through constant application of Killing Force and while it was taxing when he fought in the physical world, this was not the case here.
He felt a bit more free from the exhaustive downsides from the attacks he normally had done considering he was within his own mind fighting his father.
Believing that his father was free from the souls weighing him down didn't mean that they were gone.
They wanted to overtake Shoichi and the male was forced to see what truly happened to Tengo, he didn't fully understand everything that's happened to his father but the more and more he kept seeing what was happening it became clearer to him.
This shroud of souls carried with it a new spirit.
Obsidian himself was trying to take over Shoichi's body since Tengo was liberated from his past.