"Ju" means being natural or in other words the way which is natural and in accords with the truth of the universe and the one that human beings have to follow. Also, "Ju" may mean anything reasonable, just and honorable, accordingly noble: namely the realization of Truth , Good and Beauty.
Kyuzo MifuneThe mind, if slackened even a little, will cause defeat, the same as fearing the opponent will make you unable to use full strength.
Kyuzo MifuneA good Judoka never anticipates his action in a match, but his mind is as clever as a polished mirror which enables him to foresee precisely anything to happen and he displays freedom of his physique to cope with any change. Such mental state and physical action are called sei or tranquility and do or action, sometimes they are called ju and go or tenderness and sturdiness, in and yo or negative and positive, etc.
Kyuzo Mifune