Around a half of atoms composing protein are hydrogens. Sometimes it is a lot of fun to follow behavior of hydrogen atoms such as delocalization and unusual pKa value derived from quantum effect. The best way to discuss hydrogen behavior based on accurate position of hydrogen atoms is using neutron crystallography. We are developing a new method to obtain gigantic crystals, main obstacle to apply neutron crystallography. (Illustration, iBIX neutron diffractometer and detector system, J-PARC)