Catherine, nicknamed "Cathy," supports the romance between Polar Bear and Seal. Killer Whale (played by Ryōhei Ōtani) is Cathy's sweetheart, who is a reticent apex predator.
The anime short featuring the new characters will appear in theaters in Japan on April 5. The short was originally slated to debut last fall.
Episodes of the anime run before Japanese feature films. Shochiku previously streamed the 60-second version of the anime's first episode. The first episode debuted in Japanese theaters in March 2017. The second episode debuted in May 2017. Shochiku began streaming the "Hyōheki Don" (Ice Wall Slam) web-only short in November. A fourth episode debuted earlier in December.
Natsuki Hanae (The Disastrous Life of Saiki K.'s Reita, HaruChika's Shinjirō) voices the Seal, and Yuichiro Umehara (Mobile Suit Gundam: Iron-Blooded Orphans' Eugene, Nananin no Ayakashi's Guten) voices the Polar Bear.
Kazuya Ichikawa (Tantei Team KZ Jiken Note, Monster Strike the Animation) directed the anime at Gathering, and also penned the script. Yō Yamada (Penguindrum, The Garden of Words, your name.) served as the sound director. Rock band Scenario Art (The Perfect Insider) composed the music.
The original manga revolves around a polar bear who falls in love with an earless seal, and he wants nothing else except to protect him, even though the seal constantly thinks the bear will eat him.
Koromo launched the manga on the free manga app Comico in December 2014, and began serializing it in Monthly Comic Gene in June 2015. Kadokawa published the manga's fourth compiled book volume last April. Yen Press licensed the manga, and release the fourth volume on December 11.