UH... Occasion/Location could easily be some sort of anniversary or a plain ol' tourney and all that. Reward could be like... Well, you remember Battle City and the first chunk of Zexal was just money and rare cards, right? But the latter probably won't fly here. How about having the motivation be something like "In respect to the former titans of dueling, a massive tournament is being held to commemorate duelists such as Seto Kaiba, Yugi Muto, etc; and the winner will have a free wish of their choice granted!" or something like that? It ties in well to the original scheme you had in mind beforehand, so... Yeah.

Host could be just some random rich dude with an interest in dueling or something? I dunno.

(Is totally not going to run Nekroz on a character nope no sirree)