Masamune Dan

Masamune Dan is the founder of Genm Corp and ultimate antagonist of Kamen Rider Ex-Aid, having manipulated the events of the series to further his own goals.

Discovering the Bugster Virus
16 years ago, Masamune Dan learned of the existence of the Bugster Virus from his son, Kuroto Dan, who discovered it after it emerged from the Y2K crisis. Unbeknownst to everyone but himself, Masamune infected himself with the virus to develop an antibody for it within him.

After his son caused Zero Day and pinned the blame on him, Masamune willing took responsibility and allowed himself to be incarcerated in order to further his own goals, letting Kuroto step up to become CEO of Genm though, ubeknownst to him, his father was secretly using him to further his own goals.

Release
Masamune was eventually released from prison, allowing him to retake control of the Genm Corp. He soon showed his true colors to the Kamen Riders, revealing that his incarceration and Kuroto's succession of him had all been part of his plan.

Masamune blackmailed Hiiro into turning to his side with Proto Drago Knight Hunter Z, which had his girlfriend, Saki Momose, sealed inside of it. After much reluctance, Hiiro accepted the offer and betrayed Emu and Kuroto and prevented them stopping the Pause ability of Cronus.

With Hiiro's assistance, Masamune revived Kiriya, so he could become observant for the players of Kamen Rider Chronicle and prevent the doctors from stopping its progress. However, reviving Kiriya turned out to be Masamune's biggest mistake, as Kiriya revealed that his true purpose was to make an opening so Emu and Kuroto would create a new way to defeat him.

Cronus was later defeated by Ex-Aid Muteki Gamer. Angry at his defeat, Masamune forced Hiiro to control Taddle Legacy, threatening to kill Saki for good.

Final Battle
Following the failure of his scheme to use Gamedeus to instigate another global pandemic, Masamune finishes off Gamedeus and absorbs his remains into his body, turning himself into Gamedeus Cronus. However, the Riders all revert back to Level 1, allowing them to separate Masamune and Gamedeus, with Parado sacrificing himself to destroy the latter with the Doctor Mighty XX Gashat.

Masamune then fights against the Riders as Cronus. While holding his own at first, Cronus ends up being overwhelmed by the Riders once they switch to their Level 2 forms, with Emu delivering the final blow. However, to prevent any of the eliminated players from being saved, Masamune kills himself out of spite.