If you want inspiration for the cards, here in Latin America there is a card game called myths and legends.
I think you should redo the fanfic, using what you already have as a guide and expanding the story a bit more since it feels very rushed and not very fluid. Also, try to make the characters interact better with each other, because from my perspective, the interactions between the characters feel like an NPC conversation from Oblivion—they seem unnatural and weird.
I read the original story of this fanfic, and I can say with complete confidence that the current version is garbage. The story is super rushed, there’s zero interaction between characters, and there’s no flow to the plot. The MC goes from having 1 power to suddenly having several in the next chapter without any context. Several parts of the original story were skipped.
oc harem....
:)
Yu-Gi-Oh! Reborn As a Dark Signer!
Anime & Comics · Ezras_Hargrave