Post-nuclear Earth is barren, and life can't survive on the surface, so the few remaining people have lived under-water waiting for their time to be able to go to the surface. Amamiku and her faithful computer guardians, Pyron and Mayzamik, guard the seeds that contain the DNA for life and re-growth on the surface when the air is breathable again, but not everyone wants that to happen.

A world where it has been established that people routinely swing between slightly different parallel worlds... Koyomi Takasaki, who lives with his mother following his parents' divorce, enrolls in a local university prep school. Due to the atmosphere concentrated on studies and his social awkwardness, Koyomi is unable to make friends. One day, he is suddenly approached by his classmate Kazune Takigawa, who tells him that she has travelled from the 85th world where she and Koyomi are lovers. (Source: MAL News)

The Bobby referred to in the title is actually 17-year-old Akihiko Nomura, an underachieving high school kid with a deep love for motorcycles. His grades are failing, and his father – traditional and strict (but who must have also at some point gave in and allowed him to have a motorcycle) – is trying everything he can think of to get the kid to apply for college. His mother is so silent, she might as well not even exist. Really, his support system lies entirely in his twinkle-toed little sister, who's nosy but cheers him on in her own way. Bobby really does little else but work on his bike. He cleans his bike. He tunes up his bike. He rides his bike. One would call him a motorcycle otaku. His most recent achievement seems to have been getting photos of himself on a road trip printed in a motorcyclist hobby magazine. This leads to an unexpected result: a girl his age, who picked up that issue on a whim, decides to write him a letter. A long, rambling letter, but dreamily romantic just the same. Bobby admits to his sister that he's never gotten a letter from a girl before. He writes back, I got your letter. I'm happy 'cause it was from a girl. Bobby is not a well-rounded kid. He barely speaks – even to his own family – and the letters he writes back to the mystery girl usually consist of a single sentence or so. His obsession is all-consuming, to the point where he happily quits school to work at a biker bar. Of course, his father, at a loss, kicks him out of the house. Staying with a friend, he's delighted when his female pen pal says she'll call him. On that day, his boss at the bar decides to take him to a motocross track. But that's a day that wouldn't end in a way that anybody would expect. (Source: ANN, edited)

Tamaki Tsuru joins Aonagi University in hopes of making friends, getting a boyfriend, and living a typical university student life. She decides to try out for the tennis club in order to make friends and avoid anything too athletic. But when she is distracted by a model glider during tryouts, Tamaki ends up hitting a tennis ball right at it, smashing it into pieces. Daisuke Sorachi, a member of the Aviation Club, demands that she pay for the damages. Following the incident, Aviation Club captain Jun Kuramochi tries to goad Tamaki into joining their club, but Tamaki refuses. Not wanting to lose a chance at recruiting a club member, Jun orchestrates a way for Tamaki to earn the money to repay her debts and gives her a boyfriend in the process. While she joins the club reluctantly, Jun seems to have other plans for their newest member.