Isekai (which means another world) has been a popular theme in Japanese manga, anime, game, and light novels. The story often features the main character being transported into another world via either reincarnation or summoning. You can easily list many popular series using such a theme in recent years.
With how popular the genre has been in recent years, Kadokawa's web manga service Comic Walker and Dwango's Nico Nico Manga jointly launched a new manga contest "Isekai Comic Taisho" that is dedicated only to the "Isekai"-themed manga. Entries will be accepted from February 1 and the winning works will be serialized in both services from July 2018. The prize money for the first prize winner is 500,000 yen (about 4,500 US dollars) and the winning works are promised to be published as a tankobon book.
For the rules, The story must be original and set in a different world where the main character is transported or reincarnated. The contrary situation (from a different world to a real world) is also OK. Any genre (serious, gag, comedy, romance, etc.) is accepted. And the world must have some kind of connections with a real world (a so-called "high fantasy" story is not allowed). The work must be longer than 16 pages and shorter than 80. You will be able to submit your work via Nico Nico Manga page between February 1 and May 6, 2018.