Fantastic Racism: In this new world, the magical skills you own determine your lot in life. Your personality, character, etc. are pretty much meaningless, unless you're somehow wealthy enough to hire people with powerful skills to work on your behalf.
Genre Savvy: Kouji is smart enough to realize what kind of a story he is in, and takes advantage of the tropes and conventions of the genre.
Guile Hero: Kouji is incredibly creative with his skills, and utilizes underhanded tactics that still adhere to the rules
He searches for information about his enemies, always asks for help that he feels is necessary and creates different strategies to face his opponents, instead of relying only on his copy skill. Plus, it's nice that the skills he copies aren't so strong as the originals.
It Only Works Once: Kouji's plan to use the aphrodisiac against Marl. After he does it, the rules of the arena are updated to make such a strategy illegal, but his win is still considered valid.