from CEDEC: HAL Laboratory's Haruka Ito & Yukari Kenmochi discuss the three tenets of their approach to UI design and how they're applied to the Kirby series famitsu.com/news/202009/03…🇯🇵
one Kirby-related tidbit: Kirby's aesthetic isn't seen as "cuteness" but "warmth", and the UI reflects that warmth by deliberately avoiding points or hard edges, not using high-contrast colours, etc 
they also break from convention with regards to how they display info: using a mode selection screen as an example, they could simply & efficiently consolidate everything on one screen, but they tend towards multiple sub-screens so as to not overwhelm or intimidate new players
their 3 design principles are optimal usability, designing individual elements with a macro view of the overall aesthetic, and balancing raw usability against playful design (because, after all, it's part of the game)
I'll leave the breakdown to someone with more UI expertise
I'll leave the breakdown to someone with more UI expertise
