Ah! Who Does Big Sister Belong To?.Problems with Yggdrasil, the computer system focused on Belldandy, start to cause serious disruption on Earth. Belldandy's younger sister, Skuld, arrives to fix the system force and take Belldandy back to heaven. The goddesses hunt down the software bugs, while Skuld attempts to persuade Belldandy. As the software bugs continue to disrupt Keiichi's life, Belldandy agrees to return to heaven after telling Keiichi that time travels differently there, and that one second in heaven could equal hundreds of years on Earth. Keiichi promises to wait for her return, no matter what. Although Skuld is pleased initially, she comes to realize the extent of Keiichi and Belldandy's dedication to one another. With Keiichi's help, she rebuilds her "bug stomper", and with the bugs finally eliminated, Skuld announces her intention to remain on Earth, to watch over the pair.