Once he began eliminating soldiers of Falmuth by the thousands in service of his goal to evolve into a Demon Lord, it marked the official end of the “happy-go-lucky” Rimuru Tempest…or at least it should, if we the audience are to feel any sympathy at all for the scores of human beings he’s coldly murdering.
Meanwhile, Archbishop Reyheim—the mastermind behind this whole invasion—is spared, along with Falmuth’s King Edomalis. Folgen and Razen aren’t so lucky, getting headshotted just when the king feels like they have a shot at retreating. Even when Rimuru looms high above them with their literal lives in his fingers, Edomalis can’t help but look down on the slime.
With his soul quota at just over halfway met, Rimuru makes use of his new unique skill “Merciless”, which uses the remaining soldiers’ own lost will to fight to kill them all at once. With the requisite number achieved, the “Harvest Festival” begins. It cannot be stopped, and when it ends, Rimuru will emerge a Demon Lord.
The process also makes him extremely sleepy, so before he passes out he summons an archdemon and two underlings to fight and capture the one survivor the Great Sage detected amongst the dead, then has Ranga take him, the king, and the archbishop back to the capital, so the festival can continue in safety.
Shuna places the unconscious Rimuru atop a dais in the center of the plaza, and the Great Sage, which Shuna refers to as “Words of the World”, proceeds to give updates on the process. Benimaru hopes the Rimuru who emerges won’t “become a different person”, but…he kinda already did that when he chose this path, didn’t he?
Rimuru evolves into a Demon Slime, with vastly improved physical abilities. All of the skills he’s acquired in the past carry over or are evolved into even more powerful skills. The Great Sage also attempts to evolve, failing hundreds of times before sacrificing “Degenerate” and eventually becoming the ultimate skill “Raphael – Lord of Wisdom”.
Despite getting shot in the head by Megiddo, Razen’s “Survivor” served as an Auto-Life spell, keeping him alive. Unfortunately, he is immediately approached by the archdemon, whom he unwisely assumes is no match for him. His Nuclear Cannon is literally blown away by the archdemon as one blows a stray hair out of one’s face.
When Razen summons a spirit knight, the archdemon casually sidles up and smashes its core, destroying it in the blink of an eye. Turns out while spirits are typically superior to demons, the age and experience of the summoner matters, and Razen is still “far too young”. When Razen realizes nothing he can do will put a scratch on the “primordial” archdemon, he passes out in fear.
Meanwhile, in the plaza, the evolution is complete, and Rimuru’s closest companions are bestowed with a “gift”—which they can sense makes their connection to him even stronger. Like Rimuru when the Festival began, they all pass out from the process, but Rimuru regains his familiar human body, only now he features scarlet eyes.
Speaking with what sounds like a combination of his voice and that of the Great Sage (sorry, Raphael), he uses his new skill Beelzebub (basically Gluttony on steroids) to collect all the magicules within the anti-magic barrier, then separate them into individual souls which hang over all of the corpses.
When the archdemon returns to his side with Razen, and says there are still insufficient magicules to revive everyone, Rimuru is prepared to expend his own life energy to make up the difference. The archdemon informs him that such a sacrifice is not needed; his two underlings will gladly sacrifice themselves instead.
Rimuru accepts the offer, and the ultimate secret art of Spirit Resurrection commences. Mjurran is amazed by what she’s witnessing. Grucius knows Lord Carrion could never match this power. The archdemon is determined to become Rimuru’s subordinate “at any cost”.
Rimuru/Raphael then repeats the “3.14%” chance of successfully reviving the dead, estimating that number should be revised quite a bit upward since the probability was calculated before he attained Demon Lordship. Sure enough, the wounds of the corpses are healed, Shion’s hand moves, and her eyes open.
Rimuru has achieved everything he set out to do in this operation. With the exception of the archdemon’s fight with Razen the action in the episode was minimal, replaced by the procedural formalities inherent in such a momentous evolution. And all it took was for Rimuru to become the very thing the humans of Falmuth feared he would. Will it be back to business as usual in Tempest, or will there be any ethical or karmic blowback?