Work cat: The boy and the beast, 2016 (summary: "When Kyuta, a young orphan living on the streets of Shibuya, stumbles into a fantastic world of beasts, he's taken in by Kumatetsu, a gruff, rough-around-the-edges warrior beast who's been searching for the perfect apprentice. Despite their constant bickering, Kyuta and Kumatetsu begin training together and slowly form a bond as surrogate father and son. But the unlikely pair will be put to the ultimate test; a final showdown") (OCoLC)947734192

Leda. Genmu senki = The fantastic adventure of Yohko, 1997 (summary: "When high school student Yohko Asagiri discovers that a song she wrote opens a corridor to an other-dimensional world, it is up to her and Leda, a legendary warrior, to make sure that this corridor is not used to invade the Earth") (OCoLC)39211128

TV Tropes, viewed July 28, 2023 ("In Japanese media, this is known as 'Isekai' with such protagonists typically being their local demographic's flavor of hero, and usually involves said character gaining RPG-like powers on arrival (or at the very least, is set in a Role-Playing Game 'Verse)"; "the majority of isekai stories as we know it are derived from Web Serial Novels or old stories reworked into Light Novels, with their premises and writing style even being noted as a subgenre: Narou Isekai... In Literature, this is often referred to as a 'Portal Fantasy'")

MyAnimeList, viewed Sep. 28, 2023 (Anime > Isekai) https://myanimelist.net/anime/genre/62/Isekai

Muhamed, F. Rewriting your own narrative : Isekai as a contemporary coming of age tale, 2020: p. 1 ("Shungiku Okapi defines the modern isekai as a story in which an 'average Japanese person is teleported to another world, where they achieve all different kinds of success. They achieve a lofty status, fame, treasures, power, and a fulfilling life, in which everything is smooth sailing.' In addition to the otherworldly journey, a tale of sudden, extreme growth has become a hallmark of the genre, one that fans actively seek out") (OCoLC)1192498574

Price, P. S. A survey of the story elements of Isekai manga, in Journal of anime and manga studies, v. 2 (2021): p. 60 ("isekai is ... a subcategory of speculative fiction stories in manga, anime, and light novels") p. 69 ("The concept of the 'cheats' in isekai stories is borrowed from the mechanics of the coding of computer games") p. 72 ("There is no grand narrative to isekai stories. Instead, the hundreds of individual stories follow a common set of plot points (e.g., life prior to entering the isekai, entering the isekai, the nature of the isekai, transformations of the protagonist, and motivations in the isekai) and only differ in the specifics of how the elements occur") p. 82 ("While computer games have a tremendous influence on isekai stories, the stories usually subvert traditional games' storylines rather than simply repeating them") p. 83 ("In addition to subverting plots, the stories subvert the basic assumptions of the standard game worlds" like preferring achieving "personal goals" rather that being a "hero")

Pagan, A. A beginner's guide to isekai, July 15, 2019, via the New York Public Library blog, viewed July 28, 2023 ("Isekai is a subgenre of fantasy in which a character is suddenly transported from their world into a new or unfamiliar one"; also called "'trapped in another world manga.' That phrase hits on the core difference between isekai manga and other adventure stories. In isekai stories, the main protagonist must be either physically/mentally spirited away to another world, or reborn into this new world in a new form more powerful than their previous one.")

Why are there so many isekai/parallel world anime?, Jan. 31, 2017, via Anime News Network website, viewed Sep. 14, 2023 ("'Isekai' means (roughly) parallel world, and has come to denote the sub-genre of story in which a person from the real, mundane world finds him or herself in a radically different world; this parallel reality often has monsters and magic, and broadly resembles an epic computer or console RPG, only with unlimited processing power")

Isekai, via Wikipedia, viewed Sep. 28, 2023 (term translates to "different world," "another world" or "otherworld"; "subgenre of portal fantasy")

Established January 2024.