In the past, giant subduction-zone earthquakes and their accompanying tsunamis have caused significant damage, and it is our earnest desire to scientifically elucidate how they occur. We are the first to directly study seismogenic faults along a subduction zone at the Nankai Trough. Great earthquakes and tsunamis have repeatedly occurred at the Nankai Trough, and more are predicted at this site in the near future. Super-deep drilling by the drilling vessel “Chikyu” will enable us to directly sample seismogenic faults as well as conduct analyses, experiments, and in situ borehole measurements. These efforts should significantly improve our understanding of pre- and co-seismic processes of great subduction-zone earthquakes.