Agreed. Good post.Damn good episode overall. I think key for me is expanding on the Guizhang/master Chen relationship, and the more explicit framing of the Chens' "illicit organisation" compared to the games.
The way in which "underworld" is used in this episode also kind of feels symbolic of the framing of the Guizhang/master Chen relationship here, particularly if we consider the meaning of "underworld" as "land of the dead": Guizhang is trapped in a place he cannot leave, as a "subordinate" instead of a son, and the father/son relationship can only be restored on the day, "we leave the underworld" which is the "day we die"; (the symbolic underworld becomes real.)
It's a difficult distancing strategy from Chen, presumably to keep Guizhang on the level with the dangerous nature of their organisation - to try to protect Guizhang from bring emotionally compromised. It works nicely later on however when Ryo's commitment to Iwao inadvertently exposes Guizhang's suppressed feelings towards his father: Guizhang deep down honours his father in the same way but isn't allowed to show it, but clearly Ryo is pushing him to break with this distancing somewhat.
Again, I think it really adds some more depth to the Chen and Guizhang relationship that was arguably a bit less explored in the games: Guizhang now has more overt incentive to ultimately side with Ryo as we have a clearer understanding of why he would be empathetic towards Ryo's desire to honor his father. Another example for me that the writers have really put some thought into adapting and adding to these characters.
These are elements all running under the surface of the games too, which tells me they've really done their homework to identify them.