I don't know if it has ever been mentioned in the anime (or maybe I just don't remember), but what exactly happens if you forge a contract with a dragoon? I've tried searching it in google and had no luck using the title as the parameters. The wikia doesn't say much about it, only that it requires an exchange of flesh to be formed.
Nearing the end of the second season, Toru finally forged the contract with Fredirika, and we can see regenerative abilities but not much else. What advantages and disadvantages are there in forging a contract with a dragoon? Considering how long Toru delayed it, there must be a reason why he chose to do it at the last minute. This may be explained in detail in the LN which I haven't read.