S1.E8 ∙ Nankai no daikessen

An unseen evil lurks in the streets of Paris. Unless something is done, the darkness will unleash its destruction and consume all that is good. The City of Love will be lost to her people forever. All hope rests within the hearts of five young ladies. The only problem is, they don't even know it yet. But will an apprenticed nun, a reserved aristocrat, a hardened criminal, a traveling circus emcee and a Japanese girl experiencing loss set aside their unique differences and come together as one for the defense of many. The Paris Fighting Troup is born.

Hayate is still working as the Sanzenin Butler and this season features a lot more Hinagiku, as scenarios that include herself and Hayate allude to potentially mutual feelings between them. Nagi is also interested in escalating her relationship with Hayate, since Nagi's perception of her relationship with Hayate remains based on the miscommunication that occurred on their first meeting.

To combat the terrorist organization known as "USR", eleven countries combine their naval forces to form the Peace-Keeping Navy (PKN). 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 (a.k.a. "Snapping Turtle") 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.

A killed detective's mind is transferred by a scientific genius into the body of a shape-shifting robot superhero who fights crime.