WARNING: The following contains spoilers for Episode 6 of The Strongest Sage With The Weakest Crest, "The Strongest Sage Leaves The School," now streaming on Crunchyroll.
The first five episodes of The Strongest Sage With The Weakest Crest have primarily focused on Matthias "Matty" Hildesheimer getting used to his new body and his new crest after inducing his reincarnation thousands of years prior. In his past life as Gaius, Matty had a single crest and a reputation for being one of the most powerful sorcerers of his time. Gaius was greatly feared by demons and had a best friend named Reuter, who also had a strong reputation as a talented swordsman. Gaius and Reuter also met and befriended a darkness dragon named Iris, who Matty reunites with in the present.
In the current timeline, Matty admits he's not as powerful as he used to be and enrolled at the Second Academy, originally for reasons unknown. In the first episode alone, Matty made the monarch of the kingdom he resides in aware of a silent demon invasion that's been taking place under their noses. Having exposed that secret, Matty began working with the Second Academy students to erect a magical barrier that will keep the demons out and protect the kingdom's citizens from harm. To help him out with this task, Matty asked Iris to pose a transfer student to the Second Academy.
As the series progressed, Matty has been testing his new powers and abilities against the demons he's fought and has been monitoring his progress. He's also been teaching the Second Academy students more advanced magic skills, especially silent incantation. Matty later revealed in Episode 5 that it was his plan all along to help the students become powerful enough to be able to defend their kingdom on their own, while he could continue his journey to parts unknown. It is at this story beat that Episode 6 picks up.
In Episode 6, Matty fulfills his task of creating a barrier over the kingdom and sends Lurie and Alma to defend its borders against demons on their own. They do as they're told and are surprised that they've advanced to the point of no longer needing Matty's guidance. They prove to be important soldiers when they fight alongside their classmates, as they are able to hold off the demons long enough for Matty to complete his task and join them in the fight. When Matty finally joins his classmates, he along with Alma, Lurie and Iris are successful at defeating the more powerful demons.
With the kingdom now safe from danger, Matty decides to continue following the demons' trail and continue fighting them alone. The headmaster and especially Lurie lament his departure but understand why he needs to leave as the more powerful student sorcerer. To encourage Matty to eventually come back, the headmaster offers to keep Matty enrolled at the Second Academy on a special scholarship, reasoning that it would be easier for the school to continue backing him as needed. Matty accepts the offer, with Lurie, Alma and Iris offering to accompany him; they get the headmaster's permission and also depart the school on a scholarship.
With the "Second Academy" story arc wrapped up, the remainder of Season 1 is now set up to function as a proper isekai story. From the ending of Episode 6, the characters will be traveling to different places and meeting new people along the way. They'll also continue encountering new demons and collecting magic stones as the story progresses, and it's implied that more of Matty's past life will be revealed as well. It's very likely that Matty will re-encounter some of his old friends and allies from his past life like Reuter, as well as old enemies. While Matty's ultimate reason for inducing his reincarnation remains unknown, that might be one of the questions that gets answered before the end of Season 1.
