Charybdis/Chronology

Demon Lord Attack Arc
Moderate Harlequin Alliance members Footman and Tear, under directions from the Demon Lord Clayman, tricked Phobio into becoming the host for Charybdis so that it could inherit his hunger for revenge against the Demon Lord Milim. In the process, the dead dragons supplied by the Majins became additional 13 flying armored sharks that accompany the colossal monster.

Treyni, Trya, and their sister dryad of the Jura Tempest Federation had attempted to stop Charybdis as soon as it entered the Jura Forest but were forced to retreat temporarily due to the immense power and magic jamming abilities of Charybdis. Rimuru Tempest was summoned to respond to the threat, and he decided on an all-out attack on Charybdis by every squad that Tempest has. Additional forces from Dwargon also arrive because Gazel considers it a dangerous situation even for Dwargon, as well as to help out his "junior as both king and Hakurou's student," Rimuru. Milim was left out of the fight on Rimuru's orders, despite her wanting to destroy it herself and her capability to do so.

In the ensuing counterattack, all of the flying sharks were killed via physical attacks, and Charybdis was then attacked directly. However, its magic jamming, ultra-regeneration, and scale swarm attacks made the fight near-impossible to win for the allied forces in that particular interception attack because, as Rimuru later notices, the allied forces didn't use the correct attack methods. Charybdis then mentioned Milim, as the target of its vengeance, which convinced Rimuru to let Milim destroy its physical body but let Phobio's host body out unharmed. Rimuru then extracted Charybdis' magicore from Phobio and isolated it in his stomach. It was Charybdis' assault on Tempest and Milim's deductions that led to Rimuru to see Clayman, as well as the other members of the Moderate Harlequin Alliance as an enemy, and Carrion as innocent.

The Octagram Soars Brightly Arc
As a failsafe against betrayal, Demon Lord Clayman prepared a trap for his subordinate Yamza. The moment Yamza truly intends to betray Clayman, a Charybdis-Fragment that Clayman secretly planted onto Yamza gets activated and consumes Yamza. During the war between the Tempest-Eurazania Allied Forces against Clayman's army, Yamza who intended to surrender and leave Clayman's forces after divulging all information to the enemy, caused the trap to be activated and Yamza was consumed by the Charybdis-Fragment which created an imperfect temporary incarnation of Charybdis from Yamza and the war's surrounding corpses. This Charybdis would eventually scatter because it lacked the core, which was still sealed within Rimuru's stomach. However even in its temporary form, it still had enough power to cause a lot of death during the chaos of the war, attacks even by Calamity-class fighters like Albis being completely useless. But before Charybdis could cause any damage, Benimaru exterminated it, proving that Benimaru himself had reached Disaster-class.

Hero Awakening Arc
In order to get Ifrit out of Rimuru's stomach so that he may serve as Veldora's personal secretary, Veldora requests Rimuru to free him. In order to do so, Rimuru grants Ifrit the sealed core of Charybdis as his new body, while Veldora grants Ifrit the name Charys.