Discovery of the Temple: Mavis' Treasure Hunt!

Discovery of the Temple: Mavis' Treasure Hunt! is an anime-only event that takes place during the Tenrou Jade arc.

Prologue
After they've set off from Tenrou Island in search for the Blue Skull Guild to retrieve the Tenrou Jade, Mavis keeps exploring the ship alongside Zera and starts interfering in the crew's work. Shortly after the wind stopped, Mavis sees a pod of dolphins and jumps impulsively in the water to join them. The young girl then rides one of them and sets off for an exploring adventure. While she's admiring the coral reefs, Mavis glances a mysterious temple on the sea's floor. She then returns to the ship and wears a Magic Diving Suit in order to search the ancient temple for treasures in an attempt to help her new friends with their financial crisis.

The Discovery
Mavis dives once again and reaches the said temple, where she recognizes the patterns on its walls from the ancient Kuril civilization. She keeps swimming around the halls until she reaches a dead end. After noticing a discolored statue, she pushes it, thus unlocking a secret shrine. She then finds herself in front of twelve huge statues with various animal's heads, facing different directions, much to her surprise.

In the middle of the shrine, she finds an altar, with ancient Kurilic writings on it's bottom, in which she assumes give a hint to a treasure. Mavis manages to understand the writings which turns out to be a warning to those who enter "the house of Kuril God". Mavis, frightened by what she has read, is attacked by a shark-like sea monster. The beast continue ramming into her, with the young girl covering it's eyes with starfishes, leading the monster to bump into the walls, resulting in critical damage to the shrine.

The beast rises once again and charges at the young girl, just to be stopped by Yuri's Magic Bombs. As Mavis takes shelter, Warrod traps the beast with his Net Launcher, but in vain as the monster breaks free and attacks the hunters, bumping into the wall once again. The three hide together, with Yuri reproaching Mavis for going on her own. As they think for a way to get out, Mavis notices something in the writing, leading Yuri and Warrod to entrust her with the translating it while they try to hold the monster away. Eventually, Mavis concludes that all the statues should face the same direction towards the altar, and so she turns the effigies' heads towards it.

All the statues are now gazing towards the altar but nothing happens, much to their concern. As the beast charges once again at them, the statues starts sinking, as the altar readies to explode. It is then revealed to be a trap set to annihilate all intruders and Mavis set it in motion. Moments later, the whole temple bursts, sending the three divers away to the surface.

Aftermath
Back at the ship, the two men reprimands Mavis whilst not forgetting that she saved them. They then show Mavis and Zera some jewelry that they got from the adventure, in which Mavis reveals that she got a gold crown too. She then asks them to use it to fund their journey.