Yousuke Koiwai is a central character in the manga series 'Yotsuba to!' (Yotsuba&!). He is the adoptive father of the main protagonist, Yotsuba, and serves as a caring and easygoing parent. Koiwai works as a translator and is known for his laid-back personality, sense of humor, and supportive nature. He provides a warm, nurturing environment for Yotsuba as she explores the world, and his interactions with neighbors and friends often drive the slice-of-life narrative of the series.