Koupen-chan debuted through Rurutea's social media illustrations on Twitter, April 4, 2017. Depicted as a baby emperor penguin, the name "Koupen-chan" blends "kotei penguin" (affirmation penguin) and "kotei" (emperor), signifying a cute, encouraging emperor penguin. This naming reflects the character's core purpose of offering positive affirmations. Designed intentionally as gender-neutral to resonate universally, Koupen-chan frequently uses the catchphrase "Erai!" ("Great!" or "Well done!") to encourage everyday activities like waking up, commuting, or staying hydrated. This encouragement forms a central identity aspect, promoting positivity during routine or challenging moments. Simple pleasures define Koupen-chan's interests, such as smelling flowers, enjoying miso soup, and appreciating nature. A notable trait involves temporary color changes after consuming beverages: pink from strawberry milk, green from matcha, and light blue from an unknown drink, reverting to original black-and-white afterward. The character inhabits an expanding universe featuring multiple variations and friends, all considered different expressions of Koupen-chan per Rurutea. Variations include Pink Koupen-chan, Aqua Blue Koupen-chan, Matcha Koupen-chan, Houjicha Koupen-chan, God Koupen-chan (watching over others from a cloud), Shooting Star Koupen-chan, and Buddha Koupen-chan (associated with temples). Supporting characters include Yokoshima Enaga-san (a long-tailed tit bird with world domination ambitions but a secretly kind heart), Adelie-san (an adult Adelie penguin with a rough temper yet strong cooking and sewing skills), Adult Penguin-san (a calm emperor penguin determined to fly), Polar Bear-san (a space-originating bear with a mysterious pocket of knowledge), Kouma-chan (a baby horse aspiring to be a racehorse), and Yatagarasu-san (a guidance crow deity). These companions enrich Koupen-chan's interactions and thematic focus on finding value in small moments. Development extends beyond illustrations to digital sticker sets for platforms like LINE, where Koupen-chan won the 2017 LINE Creators Stamp Award New Face Award. Physical merchandise includes books, manga, picture books, and the art book "Koupen Chan’s World." Collaborations expanded reach into Uchikubi Gokumon Club music videos, "Penguin Highway" movie promotion via comic strips, themed food at Lotteria, NakaU, MG Cafe, Mo’s Burger, and The GUEST Cafe and Diner (featuring retro Americana decor), a New Ginger product partnership with Iwashita Foods, and limited-time train decorations on Seibu and Hankyu railways. Video game appearances encompass mobile apps "Koupen-chan's Room" and "Koupen-chan Hanamaru Weather," plus the Nintendo Switch title "Let's Play Together~♪ Koupen-chan." Animated adaptations began with short, non-narrative YouTube clips designed for warmth and comfort. A structured television anime slice-of-life series launched in April 2025, featuring Koupen-chan and friends in everyday scenarios focused on appreciating small joys, reinforcing the character's role as a source of gentle encouragement and positivity.