A Kage (影; Literally meaning "Shadow") is the appointed leader and acting representative of one of the five ninja villages, they are generally one of the most or the most powerful and skilled ninja in their respective ninja village. In Ninja Saga, the Kage of the player's ninja village; Yudai, serves to dispense missions of various ranks at the Kage Room, it could be assumed that this practice is repeated in other various ninja villages, though it is not confirmed at this point. It seems the Kage's job currently is mainly administrative so far in the game's current stage development, very rarely embarking on their own missions, focusing primarily on the affairs of their own village, and acting as a reprsentative that speaks on behalf of their respective village.
Fire Village: Yudai
Yudai is currently the Hokage (火影; Literally meaning "Fire Shadow") of the Hidden Fire Village of which the characters reside in. All missions are directed by him and enacted by the ninjas selected to do the said mission. He is presumably the strongest ninja in the fire village due to his position. He can be seen in various missions and is always seen in the Kage Room where missions are handed out.
Thunder Village: Kojiro Nagamata
The Raikage (雷影; Literally meaning "Lightning Shadow") is the leader of the Hidden Thunder Village, however little is known about them at this point. He is the most powerful ninja in the Thunder Village. He can control the thunder. He only appears in the Jounin Exam.
Water Village: Kiramuju Sonaita
The Mizukage (水影; Literally meaning "Water Shadow") is the leader of the Water Village, suggesting he is the most skilled Ninja in the Water Village, whether this is due to his control over the water-element or his other abilties remains unspecified.
The player first encounters the Mizukage during a mission from Hokage Yudai, in which the player is ordered to deliver a warning to the water village to protect their Ninja scroll.
The Mizukage also makes another appearance during the "Relief to the Water Village", offering his thanks to the player for their continuos efforts in aid of the Water Village.
Wind Village: Sukaima Nagasu
The Kazekage (風影; Literally meaning "Wind Shadow") is the the leader of the Wind Village, it could be assumed that she is the most powerful and skilled ninja in the Wind Village, whether this is due to her control over the Wind element or other various abilities is yet unspecified.
The player first encounters the Kazekage during the Mission; "Backup Request from the Wind Village", in which the player aids the Wind Village in dispatching a number of enemy blossom ninja, who are assumed to be after the Wind Village's ninja scroll.
The current acting Kazekage is the only known female member amongst the five kages of the five ninja villages.
Earth Village: Nagasi Kojiro
The Tsuchikage (土影; Literally meaning "Earth Shadow") is the leader of the Earth Village, which suggests that he is the most skilled Ninja in the Earth Village, whether this is due to his control of the Earth element or due tohis other abilties is yet to be specified.
The current Tsuchikage holds little warmth for other villages, and believes in the independance of the Earth Vilage, believing it to be strong enough to support itself, without the aid of the other ninja villages.
During the Jounin exams, the Tsuchikage is converted to some extent to the belief that the help of others is sometimes important and not always a testament to one's weakness.
He appears to be based on the Raikage, A, from Naruto, sharing his physique as well as his attitude towards the other villages.