Lord Sadamune Oga leads Clan Oga, the reinforcements the shogun sends from the mainland to help Lord Shimura retake Castle Shimura. He introduces himself to Jin and escorts him to Shimura.
Oga personally arrests Jin after Jin refuses Shimura's adoption and accepts life as the Ghost. Once Jin escapes, Oga tells his men their clan must clean up Shimura's mess.
Image: Sucker Punch Productions / PlayStationLord Shimura
Lord Shimura is the jito of Tsushima, the shogun's appointed ruler of the island, and Jin's uncle. He raised Jin as a samurai after Jin's father died. He leads the defence at Komoda Beach and is the man you spend Act 1 trying to rescue. He also has his own Tale of Lord Shimura in the main story.
Image: Sucker Punch Productions / PlayStationJin Sakai
Jin Sakai is the samurai you play in Ghost of Tsushima and the Iki Island expansion. He is Lord Shimura's nephew and the last lord of Clan Sakai. After the Mongol landing he trades the samurai code for stealth and fear, and the people start calling him the Ghost.
Kenji
Kenji is a sake seller and small-time swindler who keeps dragging Jin into his schemes. He smuggles Jin and Yuna into Azamo Bay to free Taka, then pops up with his own three-part Kenji's Tales. In the Iki Island expansion his trouble with a smuggler is how Jin gets to Iki.
Masako Adachi
Lady Masako Adachi is the only survivor of Clan Adachi and one of Jin's allies. Her husband and sons die in the Mongol landing and the rest of her family is murdered the same night. Her side storyline, Masako's Tales, has you hunting the people behind that massacre.