The Phantom Second Teacher (幻の二人目師匠), SS from Familia Chronicle Episode Ryuu

"Thank you for coming, Cranel-san. I look forward to working with you"
"M-Me too!?"
Before sunrise, in the inner garden of the pub, Bell grasped Ryuu's outstretched hand.
Several days after the casino incident, Bell had come to fulfill his promise to train together with her in the morning. She was wearing a rough outfit and wielding her wooden sword, while he was wielding a bladeless knife used for training.
"I'm sorry for making you deal with my selfishness this early in the morning..."
"N-Not at all! I'm glad I can train with strong people like you!"
While flustered, Bell stated truthfully that "he wanted to become stronger". It would be extremely beneficial for him to train with a strong former adventurer like her in order to catch up to the person he admired.
(Since I've trained with Ais-san before, this would make Ryuu-san my second teacher)
As he laughed to his own thoughts, Ryuu, who was facing him, narrowed her eyes.
"Those are good eyes...that's right, you have to be strong if you want to stand next to Syr"
"I was originally going to have you train with me, but I've decided to change plans. We'll be having a mock battle, which will help you as well."
On top of not understanding what she meant, he felt an incredibly ominous feeling, but it was too late.
"-here I come"
With her words, the Elf's strict training began.
Bell didn't remember much past that point.
"Get up. Next"
"What are you lounging around for? Next"
"The enemy isn't going to wait for you. You'll die. Next"
Before he knew it, he'd been beaten up, and was sprawled on the cold ground.
(Ryuu-san's also Spartan...)
Despite becoming Level 3, the boy easily lost consciousness from the Level 4 Elf's attacks.
"......I went too far"
""I went too far" doesn't do it justice! It's on a completely different level!"
As Ryuu silently looked down at the ragged boy, Syr arrived in 20 seconds after hearing the employee's cries and began chastising her.