The fourth volume of the Oh My Goddess! manga covers chapters 24-30. For it's initial release by Dark Horse Comics, this volume was subtitled "Love Potion No. 9".
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!
Half-goddess, half-demon, Belldandy's big sister Urd continues her campaign of naughtiness when she brews up a luuuuuv potion that, of course, goes horribly awry, infecting everyone but her poor intended target—Keiichi. But random passion in the streets may be the least of the gang's worries as a seemingly harmless CD could turn out to be a portal from the underworld, unleashing a most pesky demon, and any other random nasties that happen to be near her!
Chapter List
The Flying Motor Club
The Motor Club discover the parts of an prototype World War II aircraft and plan to get it flying for Nekomi Tech's next campus festival.
Let's Take the Love Seeds
Urd accidentally drinks a love potion she made for for Keiichi and Belldandy and proceeds to fall in love with anyone associated with plumbs.
The Nemesis
A Demon named Mara has come to Earth to sew discord for the Goddesses, and she targets Keiichi and turns him into a newt!
Mara's Counterattack
After Keiichi returns to his original form, Mara teams up with Sayoko to steal the Gods CD from the temple, as that's the one tool that can defeat her.
Balance-Ball Armour
Mara's next plan is to trick Keiichi into unbalancing his spirit and getting Belldandy to leave him.
The Worst Day of a Demon
Mara accidently loses her memory right after transforming Megumi into a car, and Keiichi, Belldandy, and Urd have to restore it since only she knows the password to turns Megumi back to normal.
Engine O' Mystery
The Motor Club participates in an fuel-efficiency race against Aoshima's Four Wheels Club, and Keiichi learns about "trolls" which work inside internal combustion engines.