Over the next ten years, he moved into a senior role within the company, working on Castlevania: Symphony of the Night as a programmer, writer, and assistant director.

In 2014, Igarashi left Konami to later become the co-founder of Artplay who in June 2019 released Bloodstained: Ritual of the Night, a spiritual successor to the Castlevania series.

[5] He worked as a programmer and was tasked with writing the story for Tokimeki Memorial, a dating sim for the PC Engine's Super CD-ROM² System.

[2] Igarashi informed his boss that he had no desire to work on a sequel to Tokimeki Memorial, and requested a departmental transfer.

The strong sales of the game prompted his boss to agree, and Igarashi asked to join the Castlevania development team.

[7] Igarashi's next project was the PlayStation game Castlevania: Symphony of the Night, where he worked on scenario writing and programming.

[10][11] The game was well received critically, later serving as an influence on the "Metroidvania" genre, though it did not translate into strong sales.

[8] After the release of Symphony of the Night, Igarashi was director for the 2000 PlayStation role-playing game Elder Gate.

[14] This included bringing back artist Ayami Kojima as character designer, who had previously worked on Symphony of the Night.

[14] During his time at Konami, Igarashi was often seen wearing a cowboy hat and brandishing a leather whip which he brought along with him to media events such as the Electronic Entertainment Expo.

[16] In March 2007, writer Warren Ellis announced that he was working on a straight to DVD animated film adaption of Castlevania III: Dracula's Curse along with Koji Igarashi.

[30] Drawing inspiration in Keiji Inafune, who had left Capcom to form his own studio and launch his new game Mighty No.

[3] A month prior to the launch of the kickstarter campaign, Igarashi filmed a pitch at Castello di Amorosa in Northern California with the help of 2 Player Productions.

[20] Launched in May 2015, Bloodstained: Ritual of the Night – a spiritual successor to the Metroidvania style of Castlevania games – had asked for US$500,000, and was funded in several hours after its opening.

[31] It eventually raised US$5.5 million, making it the most successful video game on the Kickstarter platform until Shenmue III broke this record about two months later.