Tsuruoka Itto, unmarried at 32 years old, just started a job as the janitor at an all-girls' high school, where he's found the girl he's sure he's going to marry, Asahimura Sayaka. When he hears a scream out behind the school one day, he finds Sayaka-chan fretting about a frog inside her clothes, a problem compounded by her frog allergy which soon causes her to faint. Neither the teacher on the scene nor Sayaka's friend will touch the exotic-looking pink frog for fear of poison, which leaves Itto to put his body on the line to save Sayaka-chan. When he finally manages to fish out the frog, it's latched onto a cut on his finger and sucking his blood. Itto in turn soon faints from blood loss, and when he wakes up, he's going to find himself a whole new man...

To combat the terrorist organization known as "USR", eleven countries combine their naval forces to form the Peace-Keeping Navy. However, all hell breaks loose when Admiral Red and his USR submarine UX crash the PKN's inaugural ceremony and destroy majority of the fleet. At the last minute, when the UX lands the final blow on the aircraft carrier Apollo-Norm, the obsolete Japanese submarine 707 appears from out of nowhere and sacrifices itself to save the PKN flagship. Six months later, Captain Youhei Hayami is called back to duty to lead a new group of recruits and captain an all-new 707 in the war against terrorism underwater.