As for other significant story prizes over the history of the game...
Oni no Okura : The redeemed Oni came about largely due to the efforts of various corrupt Lion players.
The Kitsu Tombs: Was a direct result of David La winning Gencon with a Lion deck containing Oni no Akuma
Having various cards credited to the winners of various events. In the later days of the game, these credits appeared on the cards themselves. Here are the cards for Aaron Barto and Chris Russell (on which they hilariously misspelled his name) who were part of my local gaming group.
The Rain of Blood thing, which was referenced above, was also a pretty cool concept in my opinion. AEG printed out a long list of currently living characters. The way it was advertised was that the winner of each tournament could choose a member from the list and that person would either be sent to The Imperial Court or Daigotsu's Court. Half way through the tournament season, the list was updated with a bunch of new names. What this really meant was that tournament winners got to decide who on that list would be saved, and who on that list would be tainted and turned evil. There was a lot of sparring over characters (Bayushi Kwanchai was saved by a matter of hours, which seems appropriate) and I, at least, thought the whole thing was a lot of fun.