He didn't really care about everything stated there, except for one point. In return for his loyalty, the man, Luca Winter, would help heal his daughter, his one and only reason to live after he lost his wife.
One of the papers clearly states her daughter's symptoms and condition. If he agreed to be Luca's puppet, he would get the method to heal his daughter. The man guaranteed that he knew his daughter had diseases.
And Sora actually believed him because although he only meets his daughter once a month, he could see the improvement of his daughter's condition from her rosy cheek, her sparkling eyes, and her noticeable weight gain.
His brain filled with the memory when he saw his daughter for the first time.