Lupin & co. attempt to steal two face plates from millionare Michael Sizuki, thinking that they will lead to an ancient treasure when brought together. However, it soon becomes apparent that there is more behind the plates then meets the eye. 

(Source: ANN)

Two jewels are the key to the ancient treasure of Yaobikuni. But legend has it that the only person who can find the treasure is one who can walk the path of death.

And why is Lupin interested? This is the one treasure his grandfather sought but did not steal.

(Source: AniDB)

The tests have come, and Keitaro can only hope to succeed. However, in the final stretch, he fails miserably and daydreams through the test. Assuming that he has failed, he runs away, so the rest of the cast hunts him down on a remote desert island to bring him back. The Toudai entrance exams have finally come (again) for Keitaro. With all his confidence Keitaro sits for the paper, but ends up falling asleep and dreaming about Narusegawa. Waking up with barely any time to complete the paper, Keitaro thinks he will fail the paper and tries to escape from Hinata Lodge and forget all the memories with it. By a stroke of luck he meets Seta, but ends up in a faraway island with the whole cast trying to look for him. (Source: ANN)

In a world covered by an endless sea of sand, there sails an island known as the Mud Whale. In its interior lies an ancient town, where the majority of its inhabitants are said to be "Marked," a double-edged trait that grants them supernatural abilities at the cost of an untimely death. Chakuro is the village archivist; young and curious, he spends his time documenting the discovery of newfound islands. But each one is like the rest—abandoned save for the remnants of those who lived there long ago. For the first time in six months, another island crosses the horizon, so Chakuro and his friends join the scouting group. During the expedition, they find vestiges of an archaic civilization. And inside one of its crumbling remains, Chakuro discovers a girl who will change his destiny and the world inside the Mud Whale as he knows it. [Written by MAL Rewrite]