Sekai to Sekai no Mannaka de

The gameplay in Sekachu follows a branching plot line which offers pre-determined scenarios with courses of interaction, and focuses on the appeal of the female main characters by the player character. The game was a commercial success at the time of its release; however, sales declined later on that year.

• Title — Sekai to Sekai no Mannaka de • Developer — Lump of Sugar • Publisher — Lump of Sugar • Platforms — Windows • Genre — Eroge, Visual novel, Bishōjo Game • Modes — Single-player

• Illustration — Average dialogue and narrative in Sekachu depicting the player character Renri Ōmi talking to (from left to right): Ataru Nishō, Minori Tsukidate, Kokoro Ōmi, Haruka Akane, and Aira Shiratori. Sekachu is a romance visual novel in which the player assumes the role of Renri Ōmi. Much of its gameplay is spent reading the text that appears on the screen, which represents the story's narrative and dialogue. The text is accompanied by character sprites, which represent who Renri is talking to, over background art. Throughout the game, the player encounters CG artwork at certain points in the story, which take the place of the background art and character sprites. There are four main plot lines (and a bonus route) that the player will have the chance to experience, one for each of the heroines in the story. Throughout gameplay, the player is given multiple options to choose from, and text progression pauses at these points until a choice is made. Some decisions can lead the game to end prematurely and offer an alternative ending to the plot. To view all plot lines in their entirety, the player will have to replay the game multiple times and choose different choices to further the plot in an alternate direction. There are scenes depicting Renri and a given heroine having sex.

Most of Sekachus story takes place during spring break in the fictional Kaginomori Academy, which is famous for its math and science courses. This prestigious academy also has a total of eighty-eight dormitories. A few students, who attend Kaginomori, are residents of the Erudeshu dormitory. The game, set in the countryside, combines harem and fantasy elements together.

voiced by Aine Sakura, the main heroine of Sekachu, is being discharged from the hospital. She is a sweet girl who is loved by everyone, and despite her weak constitution, has a bright and lively personality. Kokoro is to join her older brother Renri Ōmi, the player character, at Kaginomori Academy, and board the Erdõs dormitory. Renri is serious, but caring, and his nagging has earned him the nickname "okā-san". He and his friends decide to clean out Erdõs, for Kokoro, and while cleaning out the attic, they discover mysterious keys and incantation-like words, which are clues guiding them to a secret room housing a gigantic object. This is referred to as the "Celestial Globe" by the main characters. Another heroine includes voiced by Iroha Haruno, a beautiful and intelligent girl, appearing to be very ladylike. However, she is fun-loving outside of school. Renri makes other friends during his stay in Kaginomori, such as voiced by Haruru Aikaze, an extremely quiet girl who only seems to talk to him. Much of the time, Aira does not change her facial expression. Renri's senpai, voiced by Ui, is a genius with dreadful sleeping habits and tends to speak slowly. She has a pair of dog ears and a tail.

The production and planning of Sekachu began right after Hanairo Heptagram, another work by Lump of Sugar. The game was originally going to be called Tobira no Mukō no Sphere, but in mid-development, Celery and Tetsujin wanted to change the title, and searched in bookstores for inspiration. Later on, Tetsujin proposed the idea of Sekai to Sekai no Mannaka de, for a title. Celery directed the game, and wrote the scenario; Tetsujin and Tamaki Ichikawa also contributed to the writing. The character designer was Fumitake Moekibara, who has drawn many character designs in previous Lump of Sugar games, such as Nursery Rhyme, Itsuka, Todoku, Ano Sora ni, and Tayutama: Kiss on my Deity. The game's music was composed entirely by Shigenobu Ōkawa.

The game's official website opened on August 21, 2013. This site would update information pertaining to the self-described "heart eloping ADV", Sekachu. Before any copies of the game were released, there were two free trial downloads. The first of these was made available on November 8, 2013, and the second on December 30, 2013. Both of these versions included adult content. The game was postponed for a month before being released as a limited edition DVD-ROM for Windows PCs on January 31, 2014. A full version of the game was put up for download on the official website - this time, not for free - on October 2, 2015.

Sekachu has three theme songs: "I Want to Be Like a Star", the first opening theme, and "Recollections", the ending theme, were sung by Kicco. Aira's voice actress, Haruru Aikaze, performed "Sing a Song", the only insert song in the game. A maxi single came bundled with the limited edition's release, containing the three songs and their instrumental versions. The background music of Sekachu was released in an original soundtrack on January 31, 2014, along with the limited edition's release.