Netflix has confirmed that the new season of Aggretsuko premiere on the streaming service in December of 2021.A premiere window for the fourth season of the popular animated workplace comedy was confirmed by Netflix during their TUDUM fan celebration. While few details about the new season were revealed during the livestream, the official Netflix Anime Twitter account revealed the first image from the series' highly anticipated return, and teased new developments in the relationship between Retsuko, the series' overworked heroine, and her coworker Haida, who harbors unrequited feelings for her. The new art also depicts the return of several of the show's supporting cast, including Retsuko's nosy coworker Fenneko, as well as some new characters who will be introduced in the upcoming season.
Aggretsuko was created by Sanrio, the company behind iconic mascot characters such as Hello Kitty and Badtz Maru. The series tells the story of Retsuko, a red panda who makes a living as a low-ranking office worker at a large company. Retsuko contains all of her stress and anger during the day and can only express her inner frustrations at night, when she retreats to Tokyo's karaoke rooms to sing her favorite type of music, death metal.
The character was first animated in a series of shorts for Japanese TV network TBS. The full animated series originally debuted on Netflix in 2018, and was warmly received for its mix of cute, colorful visuals with biting, frequently too-real satire about office work and the harsh realities of adult life.  The series was a surprise hit for Netflix, and was quickly renewed for additional seasons and a Christmas special.
Source: Netflix