Bubble deformation and its outcome play a central role in natural and industrial processes. In this paper, we investigate experimentally the formation and breakup of an inertial jet arising from the relaxation of a highly deformed bubble produced by coaxial coalescence. It is found that various jets can emerge inside the bubbles with given shapes and velocities. We develop a robust scaling law to describe the jet velocity and unravel its dependence on initial bubble shape, capillary, gravity, viscosity and liquid properties. With such a model, we demonstrate a capillary-driven mechanism for the jet formation. Then, the evolution of the jet-pinching process is analyzed in detail, and we confirm two different mechanisms at play in jet breakup, namely end-pinching and root-pinching. It appears that jet breakup can be predicted well by considering the bubble Ohnesorge and Bond numbers. Moreover, in this parameter space, a phase diagram for jet breakup and no breakup is established. Following jet breakup, an interesting “Liquid in Gas” structure: one or multiple droplets encapsulated in a large bubble, is observed. We establish two different scaling laws for top jet drop radius from the perspective of bubble collapse and jet dynamics, respectively. These scaling behaviors corresponding to different parameter spaces shed light on the effects of viscous, capillary and gravitational forces on drop detachment clearly. Especially, a simple linear relationship between the drop Ohnesorge and jet Capillary numbers is demonstrated. Furthermore, we systematically establish a complete functional relationship from bubble collapse to jet formation to droplet detachment, which is helpful to control the bubble-collapsing jet.