|Appeared in||Toushin Toshi 2, Rance III, Rance 03, Rance IV, Kichikuou Rance, Rance VI, Rance Quest, Rance IX}}|
An Okayu Fever is a type of Guy Monster with a big body and a very large head. It's mostly green and has four arms with no legs, instead having some tentacle-like roots. His large face is very recognizable for having two round holes as eyes, and a similar bigger one for mouth. His favourite phrase is "Upo".
Since his head is so big, it's also really heavy and falls back, so it uses the extra-arms of his back to support it. He has a huge skull cavity, but his brain is very small in comparison, and most of the thoughts it processes are cunning, superfluous and lewd thoughts. His hands are very skilled at foreplay, and can use their hands to toy with a human woman or a Gal Monster. It also segregates a special fluid called "Okayu Poison" that serves as a very potent aphrodisiac. If a female were to be exposed by it for a long period of time, they would turn into lascive individual that can't spend too long without sexual intercourse, effectively going insane, acting like a powerful curse, but this state is only achieved after many months of sexual foreplay with the Okayu Fever.
His meat is very tough and sturdy, but in the hands of a proffessional cook it can be used to made exquisite meals.
In Battle, Okayu Fever are pretty powerful creatures. They almost always fight on their own and are very durable opponents, either using their hands to punch their opponents or potent offensive magic. However, they have below average speed and almost null evasion, since their mobility is very limited.Okayu Fever can also inflict a disease on humans called "Okayu Disease". An Okayu Fever needs to be infected with a virus, it doesn't weaken much but their skin gets a lot paler. Then, if a human were to kiss the Okayu Fever he would contract this extremely rare disease. After this, it acts with a very strong fever, and the body of the victim weakens, and they suddenly slowly and progressively start transforming into an Okayu Fever. It only starts with the transformation when the victim starts adding "Upo" to their phrases, and from this point it takes a few days until it's fully transformed.
The only way to cure it is to have a specialised medic perform a surgery with the appropiate remedies and then have sexual intercourse with the patient for hours. This is the only way known to cure this disease, and it's also noted for being the only disease that requires fornication to be cured. Only men can contract this disease, since Okayu Fever are Guy Monsters. Okayu Disease is classified as one of the most rare diseases in the world and the vast majority of doctors experience their whole lives without finding a single case.