WARNING: The following contains spoilers for Episode 2 of The Strongest Sage With The Weakest Crest, "The Strongest Sage Enters the Dungeon," now streaming on Crunchyroll.
Thousands of years ago, Matthias “Matty” Hildesheimer was a powerful sage in his former life as Gaius. Despite his strong magical abilities and talents with a single crest, Gaius still forced himself to reincarnate in order to get his desired four crests, which, in his time, was the more powerful crest to possess in combat. Ironically, this isn't still true in the present timeline where the four crests are treated as the crest of failure.
In Episode 1 of The Strongest Sage With The Weakest Crest, Matty was still a highly powerful and talented sage despite possessing the crest of failure and ended up teaching his own classmates the long-lost practices of spell-casting. He also revealed in the same episode that he does remember his past life, which Episode 2 further developed. Matty once again confirmed that he magically induced his own reincarnation, but he also revealed that his memories gradually came back as he got older.
Following his defeat of Devilis -- a demon posing as a student at the First Academy -- in Episode 1, the monarch of the kingdom he just saved decided to bestow him with land as a reward. Matty, however, declined, admitting he's not living his current life for material wealth, but to obtain more power. Instead, he settled for obtaining a new magical sword and asks to access the kingdom's dungeon in order to obtain a special stone known as adamantite in order to create a barrier that will protect the kingdom from further demonic invasion.
As he was looking for a new sword to claim as his reward, Matty came across two artifacts that belonged to his previous incarnation: the magical sword Gaius forged in the days when he was obsessed with sword making, and an enchanted necklace he also made. Matty decided to reclaim his former incarnation's artifacts and used them to test his new powers against the monsters that reside within the dungeon beneath the kingdom. He succeeded in his task by going down to the 25th floor, a floor no one has been able to access in the past, and used his new powers to defeat a monstrous serpent.
A little more is learned about Matty's motivations in Episode 2, at least as informed by his past experiences as Gaius. Since Gaius originally felt his powers weren't strong enough to defeat the demons of his time, he forced his reincarnation to gain the four crests as part of his journey to obtaining more power. He also feels that once his power levels and magical talents exceed those of his previous incarnation, he'll finally be able to stop an impending demonic invasion.
What remains unclear is how Matty even knows about the demons' plans in the first place, considering how much time has passed between his life as Gaius and his current life. In the same way, the human world has changed in the thousands of years since Gaius lived, one would assume the demonic world would've also changed as well to keep up with human evolution. At best, it's strongly implied the demons played the long game by waiting for humans to become comfortable with less magic before infiltrating their kingdoms. The bigger question remains, however, how Gaius/Matty knew about this plan in advance.
While some light is shed about Matty's motivations in Episode 2, at the same time, it remains uncertain if his motivations are entirely heroic. One of the strangest things he says during one of his monologues about his need for more power is the fact he can't have human beings going extinct before he has the chance to make himself properly strong. He also says he will need to keep working with them "for a while," which doesn't indicate he has humanity's best interests in mind, only his own. At best, Matty's motivations appear heroic on the surface, but something else might be lurking underneath.
