Leon never thought of creating a contract with anything. Summoning magic was like that, but at the same time, magic contracts were a lot more restrictive even though they granted some freedom to both parts.
The very moment Leon accepted the terms, some magic words appearing in his right arm. Although they weren't words of Earth, he could understand their meaning since the contract was bound with his soul, just like it was with Tyrselle. The first topic of the contract was that Leon and Tyrselle would work together to reach a future which they could feel satisfied with. It was a bit vague for his tastes, but at the very least, it granted him the chance to reach a middle point between his goals and Tyrselle's.