During a summer camp, 15 children, 8 males and 7 females, find a grotto by the sea. Deep within they discover working computers and some electronic equipment, and later the owner, a man called Kokopelli. Kokopelli claimed to be a programmer working on a brand new game, in which a large robot has to defend the Earth against fifteen alien invasions. He persuades the children to test the game and sign a contract. All but one of them signs, barely a moment later they mysteriously awaken on the shore believing what happened was just a dream.
(Source: ANN)
An extra story called Bokurano ~Mō Hitotsu no Bokurano~ (Yet Another Bokurano) will run in Ikki the issue after the end of the main story.

It's mainly about two different armies battling each other out with their mechas. (Source: mangaupdates)

From Kotonoha:
In his second collection of short stories, Mohiro Kitoh recounts the tragic fates of people living in a half-futuristic, half-fantasy city whose inexorable structural decay seems to be mirrored in its citizens’ hearts.

Mariko Kazunori ("Nori") is a 28-year man who hated bicycles until he almost runs over road-racer Oda Rin. After meeting with her and her weird family, everything goes wrong for this pitiful hero. His license gets revoked and he is forced by his friends to start bicycling.

The story takes place in a world that resembles 19th century Europe. When a carnival comes to town one day, Ray, the son of a bar owner, meets a girl with wings. The girl's name is Vendemiaire. She was given life by her Creator and tells Ray that she is not human.

This is a series of short stories showing the kindness and cruelty of mankind. You can enjoy pictures drawn with a fine touch alongside the philosophic dialogue of the characters.

This 2-volume series is the debut work of Mr. Kitoh. Hints for his next work, Narutaru can also be found in this story.

(Blurp above from Kodanclub)

The story takes place during the 2595th year of the Ko (Light) Era. Ko, the country of the rising sun, invaded several countries and war rages. Its territory does not stop growing and in heaven, the battleships are a legion. Gaw, a young immigrant boy, and Fa, a mysterious young girl, will find themselves embarking on this "war."

(Source: animeland.com)

From Mohiro Kitoh, the author of Narutaru and Bokurano, comes this wonderful collection of short stories that reinforces his reputation as a skillful story teller. Spanning almost 20 years of the artist’s career—from his professional debut work Zansho to his latest contribution to IKKI magazine Pochi no basho—this collected volume offers a unique view of Kitoh’s artistic development.

Included are such stories like Pochi's Place.

The story could basically be split into two halves. The main story is about Tamai Shiina, who is an energetic middle-school teenage girl. She visits her grandparent's over the summer where she runs into a very strange creature. Shiina has had lots of strange dreams as of late and also when she was younger, and this strange creature is somewhat related to her visions. She names the small cuddly star-shaped creature, Hoshimaru.

Little did she know that this cuddly creature is really part of herself. After her vacation, Shiina goes back to her home, living with her father. She runs into other children with similar creatures the following days. However, these children have developed their creatures, and they have complete control over them. They mostly use these creatures for their own destructive pleasure and not for good. There is a group of teenagers that all have these strange creatures, and they plan to basically conquer the world, creating a utopia of whatever they desire. Will they succeed? Will Shiina ever develop Hoshimaru?
Taken from thespectrum.net