Metal Release: Jack in the Box

The user manifests a rasengan, encasing it within a cubical structure, then proceeding to throw the box at their opponent. The technique has a time limit, where after the given time, chosen entirely by the user of the technique, it will detonate, resulting in a horrific explosion. As a combination of both the metal release and the rasengan, the technique is incredibly potent, used only for measures of murder.