| Night Lesson & Prison Lock|
|Publisher|| Fujimi Shobo (JP)
Yen Press (US)
|Magazine Issue||Monthly Dragon Age March 2011|
|Release Date||February 9, 2011|
Night Lesson & Prison Lock is the third chapter of Trinity Seven, initially serialized in Monthly Dragon Age March 2011 issue on February 9, 2011, and later compiled in the first volume on July 7, 2011.
Finding himself with Lilith, Selina and Levi in his room, Arata questions the girls for the reason of their presense. Levi and Selina both reply to collect data, while Lilith insists that she is there to monitor them as a teacher. After answering questions and teasing Lilith, Arata then asks her about the grimoire Hijiri entrusted to him. Lilith reveals the grimoire as the legendary Astil Manuscript, said to contain information of another world, greatly surprising Selina and Levi.
Suddenly, the room begins shaking and a blackout to occur, causing Arata to accidentally fall and grope the girls. After the Astil Manuscript provides lighting and the girls punish Arata, they find themselves trapped within the room due to a barrier created by an unkown individual. Despite the Astil Manuscript having already figured out the puzzle to escape, the grimoire decides to let them discover the solution themselves. Despite the situation, Arata remains calm and focused, noting that the only issue is the lack of a bathroom, much to Selina's dismay. Neverthess, Arata attempts to force his way out first by smashing a chair against the door as magic is not restricted by common sense, temporarily startling the girls although they quickly realize his thinking.
However, after a while, their search yields no results and Lilith is revealed to be reaching her limit, soon followed by Levi and Selina. In a final attempt to escape their predicament, Arata, Selina and Levi manage to trick a half-awake Astil Manuscript in revealing the location of the source of the barrier. After destroying the seal, the girls manage to avoid causing an accident while the Astil Manuscript is impressed with Arata's cleverness, as well as having looking forward to him choosing his Thema.
Meanwhile, outside of the dormitory, Arin senses that they have destroyed her barrier, revealing her to be the culprit. The Headmaster, who was also observing Arata's situation with Arin, asks her if Arata will become an evil magus although she is unsure. Regardless, impressed by Arata's performance, the Headmaster comments that he looking forward to seeing if he will become the next Magic King, as well as the partner of Arin.
- Arata's favorite food is revealed to be fried chicken.