Leon was very familiar with the Bottomless Abyss; truly, the Bottomless Abyss was too iconic.
The Bottomless Abyss is the home of demons dedicated to death and destruction, embodying all that is rebellious, terrifying, and chaotic. Its almost endless layers spiral downward, forming increasingly horrific forms.
Each layer of the Bottomless Abyss has its own peculiar and terrifying environment, yet they are all equally harsh and uninhabitable, each reflecting the chaotic nature of the Abyss. In fact, most things people see or touch in this plane appear to be in a state of decay, fracture, or corruption.
As a Red Dragon, Leon wasn't as opposed to the Bottomless Abyss; since he was here, the Joseph Garden could hone his combat skills, and the Bottomless Abyss was not much different.