Hello!

As far as I remember, you need to have 7 Kyushoku Deer Scrolls and 10 Contracting Scrolls for you to be able to summon it. My memory is kinda blurry already since I virtually summoned that one long time ago.

In addition to this topic, Kyushoku Deer Scroll is also obtainable from Decisive Bonds by chances when you open Treasure Boxes from winning battles while the Contracting Scrolls are obtainable from Events and/or Cross-Server Great Ninja War Packs. Thank you.