He decides to follow the proper academy guidelines and punishes them appropiately.

Byleth was having an long internal discussion with himself over what to do with the streaker girls in front of him, and how should a good teacher respond to this problem. Taking advantage of the situation, Annette and Mercedes tried to leave the room without him noticing, only for him to suddently remember about the existence of his teacher handbook.

"I know, let's check the handbook", exclamed Byleth as he grabbed the handbook from his bad, making the two nude girls stop in their tracks as he put his view upon them once again.

"Well...let's see, i don't know if there's something in this book about public nudity, but let's check either way,", Byleth said to Annette and Mercedes, upon which, he began to read the book, while the two girls could only see each other and gulp as they awaited for the worst.

"Let's see..., let's see, emmmm..., ahhh, there it is!", he exclamed as he finally arrived to the relevant section of the book, putting Annette and Mercedes more and more nervous with each passing moment.

"Ok then, i will read it for you", he said, " 'As a holy and civilizated place of learning, it is absolutely forbidden for either students or faculty to be in position of public indecency inside the academy, whether through the use of too revealing clothing, realizing sexual acts in public, or being naked outside of the designatec bathing areas or personal dorm of one", he explained.

"As for the punishment or diciplinary sanction reserved for violating one of this rules...., let's see, let's see...,", Byleth said, as he searched for the appropiate punishment for the two, at the same time, Annette and Mercedes were sweating as they prepared themselves for the answer.

After another round of searching, though, Byleth eventually arrived to what he wanted to know, and began reading it loud for the girls to hear. "emmm....,here it is, for public nudity it shall be...",