The inventory is used as the first screen of the player menu which navigates to all other screens. This takes inspiration from Bungie's Destiny inventory interface and Bethesda's Skyrim player menu compass.
The skill tree is separated by skill, with classic skill nodes. More needs to be developed on how total stats work and affect what skills you can upgrade. The mechanical arm is present there as the main source of power in the context of the game. Looking to use God of War as reference to simplify in the next iteration
The journal focuses on being semi-diegetic to promote a bit more immersion within the interface. This is also why the bestiary is contained here too. Tabs act to separate categories clearly within the physical journal.
I was recently inspired by my playthrough of God of War. I found parallels to my sketches for the journal and skill tree but more simplified and refined.