Seisui is a substance that sustains life. It has the power to heal any damage taken by body, that includes diseases, cuts, bruises etc. One bottle of concentrated seisui is very expensive. It was shown later on the series that one drop of highly concentrated seisui is enough to heal thousands of minor pains and diseases. Normally, seisui is distilled as the process to extract one drop is tedious. Seisui also provokes wars because of its elevated price and value given by society.
Just as much as it does good, it does bad. Researchers were able to take seisui and apply it in a contraption that causes a huge explosion. This explosion is comparable to that of an atomic bomb.
Organizations proven to have the seisui bomb: