Originally, when Reimu and Marisa were koyukkuris, they were purchased as pets by a Big Brother. At that time, they were enjoying warm mister bed and lots of sweet sweets every day. Big Brother took care of them carefully, and so they firmly believed that they were Chosen Yukkuris.
The two yukkuris grew rapidly under Big Brother's unwavering care. Not half a year after being purchased, the two koyukkuris were already adults. Their urges grew along with their bodes, and Reimu and Marisa began to look at one another with adoring eyes. Finally, one day, after rub rub, the two refreshed for the first time. And so before the first year was over, Reimu was preg~gers.