The Phantom Second Teacher (幻の二人目師匠) is a special story from Familia Chronicle Episode Ryuu.
In the Hostess of Fertility's inner garden, early in the morning, Bell and Ryuu greeted one another, having come to fulfill their promise to train together. Ryuu apologized for having Bell help her, but he denied stating that he was glad to be able to train with a strong individual. He genuinely wanted to become stronger to catch up to Ais, and laughed as he thought about how Ryuu would be his second teacher, with Ais being his first.
Meanwhile, Ryuu approved of his resolve to become stronger, affirming that he needed to grow if he was going to be with Syr. Bell was caught off guard by Ryuu's sudden words, and even more when she declared that instead of training they'll do mock battles so that he benefited more from it. Not able to process what she had said, Bell had a bad feeling, all too late.
Ryuu, declaring the start of training, attacked him with a strict teaching method in place, making Bell reflect that Ryuu was also a spartan style teacher. After being knocked out several times, Bell was left lying in the floor while Ryuu recognized that she had gone too far, with the other employees giving an outburst in reply. As Ryuu looked at the beaten boy, Syr arrived 20 seconds later and began chastising her.