Lupin III: Twilight Gemini no Himitsu

ルパン三世『トワイライト☆ジェミニの秘密』

A dying mob boss entrusts Lupin with a diamond that supposedly is the key to a vast treasure. But when Lupin is attacked by an assassin and saves a mysterious girl from trouble, it becomes clear that that there's more to this treasure then meets the eye... (Source: ANN)