Idia’s favorite food is listed as “sweets” in his EN profile, but originally it is “dagashi,” which can also be savory.
They are very cheap snack foods primarily targeted at children, things like hard candies/gummy candies/rice crackers/etc.
Idia specifies that his favorites are 知育系の駄菓子 (DIY dagashi kits), where you mix gelatins and things together to create something yourself.
Idia says, “There’s something genuinely engaging about being able to change the shape and color yourself. It’s definitely not just for kids, okay?”