Champions who rely on a specific item that no one else can viably use.

Sounds like an Akali thread.

Garen and Atma's

Kayle and Runaan's Hurricane. Well maybe. Kayle can get away with not building it but she does the most with that item in any case.

lb, veigar pretty much rely on dfg to be viable (and i know that dfg is viable on tons of champions)

Items no one else can use and that only they can use, sounds like and