Considering the main innovation within bitcoin is the fact that it solves the problem of how to get a decentralised network to agree on a certain thing, it's strange you would even ask this.
I'd say its the "thing" and the agreement to that are the innovations.
The blockchain is what solves the problem of consensus on decentralised networks. That's the innovation, everything else had already existed. So, what would be the point of having a blockchain on a centralised currency?