The ninth volume of the Oh My Goddess! manga covers chapters 53-57. For it's initial English release, this volume was subtitled "Miss Keiichi".
Volume Description
Ever since a cosmic phone call brought the literal young goddess Belldandy into college student Keiichi's residence, his personal life has been turned upside-down, sideways, and sometimes even into strange dimensions!
When Urd and Skuld are called back to the heavenly realm for remedial training, Belldandy and Keiichi are alone at last! But two things are going to complicate their getting closer as man and woman: Belldandy has come down with a mysterious illness; and, thanks to fooling with Urd's medicine to try and cure her, Keiichi isn't a man anymore-he's a woman!
Chapters
Law of the Ninja
A second tiny ninja named Hikari infiltrates the Temple on the mission to eliminate Kodama as the latter's punishment for having abandoned the ninja clan.
Together for Never
Belldandy falls ill right after Urd and Skuld temporarily return to Heaven, and Keiichi's accidentally turns himself into a woman while testing out Urd's medicine!
Can't Stop Being Jealous
A plum tree spirit named Troubadour, Urd's former lover, suddenly appears at the Temple.
It's Lonely at the Top
Keiichi finds himself as the acting director of the Motor Club just before they compete in a hill-climbing motorcycle competition.
Tainted God
A cute freshman and amateur exorcist named Shiho Sakakibara wants to perform an exorcism on Keiichi at the temple, which puts Belldandy's trust in Keiichi to the test.