Valkyrie Drive: Mermaid

Space Patrol Luluco is a Japanese manga/anime series created by Arms (anime studios).

Synopsis
Naïve 16-year-old Mamori Tokonome is accustomed to being teased at school for having an unfortunate surname that can also be read as "virgin." However, young Mamori will soon have to get used to being teased in other ways...

Kidnapped during gym class, Mamori wakes up only to find herself stranded and under attack on the exotic island of Mermaid. Luckily, enigmatic fellow castaway Mirei Shikishima knows exactly how to take the lead—through a passionate kiss, Mirei unleashes Mamori's Exter transformation abilities, turning the innocent red-head into a battle-ready cutlass through the power of arousal.

The duo will need to tap into that power as Mermaid Island is full of potential friends and foes: Charlotte, the sadistic Liberator of an Exter harem; the gluttonous and crafty Meifon; the mysterious but charismatic Akira Hiiragi; and the erotic biker duo Lady Lady. Mamori and Mirei's powerful and intimate embrace is the only way for the pair to ensure their survival on this scandalous island.


 * Source: https://myanimelist.net/anime/30385/Valkyrie_Drive__Mermaid

Featured perfect giantess: Nimi Minimi

 * 1) She is a secondary character (supporter to protagonists).
 * 2) She was giantess on Valkyrie Drive: Mermaid - EP05 and Valkyrie Drive: Mermaid - EP12.
 * 3) She appears in Valkyrie Drive: Mermaid - EP06, but she doesn't use her giantess form. That is, there is a brief cameo.