Chen Yu naturally wouldn't take Kojo Kyoko's loyalty at face value based on her mere words.
Although Kojo Kyoko's loyalty might indeed be sincere, even samurai who were willing to die for their lord during the Warring States Period could betray their sworn oaths; verbal loyalty had no tangible binding force. If it did, there would not be so many betrayals and usurpations.
For a necromancer, the only truly trustworthy things were his own spells and the dead.
When Tsuchimikado Yoshiharu and Kyuuzai Ryousen received the inheritance Chen Yu offered, he had already marked them with restriction spells. The Promotion Ceremony further integrated these spells into their souls, instinctively preventing any thoughts of betrayal.
For a necromancer who specializes in souls, integrating a restriction spell into the soul and making it an inseparable part is merely a basic operation.
