@AMetroid That page doesn't really deal with what I'm talking about, because the contract portion I'm talking about is solely in his past life which all happens before that page (the Chapter 15 flashback: https://mangadex.org/chapter/14488/13 ). You see the moment that he forms his contract in the initial timeline via the Blood, alongside another soldier, and it's in a very controlled situation in a tent. We also see him in chapter 1, dead on the battlefield with the Blood around his neck. If the Blood was only necessary to form the initial contract, there would have been no reason to let him take it out of the tent after making the contract, and they were apparently pretty valuable/hard to develop so they would want to keep as many as they could.
Also in regards to that page, in the new timeline she'd already come out on her own in chapter 14, before he even had a Blood (which is why he thought to ask for one to be made), so if it was only needed for the initial contract there would've been no reason for him to ask for a Blood to be made in this timeline, since his contract was what dragged her into this timeline anyway. So it seems like even if the Blood is needed for the initial contract, it's still needed in order to forcibly call the spirit too. Basically like bribing a cat with treats: They're already your pet, but it's easier to make them do things with a lure.