As the increase of sensitivity necessary for the future missions, it becomes inevitable to collaborate internationally to produce giant and sophisticated X-ray observatories. Coming Japanese mission NeXT is a Japanese mission with strong international collaborations. We are considering two major instruments; the micro-calorimeter and the hard X-ray imaging system. The former should open up new horizon of X-ray astronomy, and has to be realized as soon as possible. High resolution spectroscopy is necessary to investigate the dynamics and plasma physics, more over to resolve the iron line profile from black holes. The latter will also provide us with new horizon, which is being explored with hard X-ray detectors onboard Suzaku. Newly introduced hard X-ray optics with multi-layers allows us to image hard X-ray sources up to 60-80 keV. It gives us a few orders of magnitude better efficiency and spatial information. Survey of obscured AGN and mapping of non-thermal components could be the major area we are able to explore. These issues will be thoroughly investigated with much better image quality and then higher sensitivity in XEUS and Constellation-X.