Building and operating the Hybrid Pressure Core Sampler has not all been plain-sailing. The system was developed and manufacturing itself was contracted to a manufacturer specializing in building this kind of equipment. Tests were performed, and after improving the design it was re-manufactured. The finished system was taken into actual operation at a mud volcano on the 2,000 m deep sea floor off the Kii Peninsula in June 2012. Since mud volcanoes are formed from mud spouted from deep in the earth, it is a mixture of mud, broken rock and methane hydrate, and even collecting samples in the regular way is difficult. Some of the samples hardly contained anything, even though the pressure had been preserved. But when the sample that was collected on the fifth day of the experiment was examined with X rays, an image surfaced of mud, gravel from rock that had been destroyed in the mud volcano’s eruption and brought up from the deep, and methane hydrate spread through it like a web. The internal pressure is roughly 200 atmospheres, and it is the first sample where, through maintaining its pressure, the sediment is preserved in its original subseafloor form. This is of great significance. What kinds of things happen in the subseafloor world? This system should greatly contribute to the solving of this mystery.