As the protectors of not only their people's lives, but their livelihoods, the samurai clans of Ghost of Tsushima could have spent much of their time in the game being close allies for the Ghost and the rebellion forces. Unfortunately, the majority of the clans were wiped out in the initial invasion on Komoda Beach, leaving very few members left alive by the game's end.
While this makes the rebellion that much harder for all those left alive, it does mean that it's easier to associate each clan with their particular zodiac sign, since the ones who are left alive all have vastly different personalities and character traits that make them stand out from the crowd.
12 Aquarius: Nagao
Clan Nagao is renowned on the island of Tsushima for the quality of its archers, with the greatest of them, Sensei Ishikawa, falling under their banner. Nagao's archers are also known for being uncompromising in their duties and honor, as well as having an imaginative approach to battle tactics and a deep sense of loyalty, making them a perfect fit for Aquarians.
11 Pisces: Shimura
Jin's hopeful father figure, the wise and affectionate Lord Shimura, is the perfect embodiment of Pisces if there ever was one. His familial attachment to his nephew despite their radical personal differences, as well as his somewhat misguided wisdom towards battlefield tactics, give him many personality traits often associated with the Pisces zodiac.
10 Aries: Sakai
The quick and dynamic nature of the Ghost and Jin's alter ego fits perfectly with the ram zodiac, even if it is strange to associate a masked killing machine with a horned sheep. Those born under the Aries sign are also often competitive and eager to leap into action when the need requires it, which is particularly accurate for Jin's early storming of the Khan's base of operations, even if it did end badly for the young samurai.
9 Taurus: Oga
Although players don't see much of the Oga clan, as they are only sent by the Shogun in the last few missions of the game to assist in ridding Tsushima of Khotun Khan and the Mongol army, their roles as soldiers allow them to fit neatly under the sign of the bull.
Strong and dependable, the warriors of Clan Oga fit many of the traits common with the Taurus zodiac, and their creative natures as a samurai further exemplify this sign.
8 Gemini: Sakai
If there is just one zodiac sign that represents Jin perfectly, it would be Gemini. Aside from a Gemini's versatile and curious personality, the twin zodiac is a perfect personification of the duality between the role of the Ghost and Jin's duty as a samurai. One of Jin's greatest strengths, as well as his ultimate weakness, in Ghost of Tsushima is his own willingness to subvert the expectations of his role as a man of the people, choosing to do whatever it takes to ensure the survival of his island home.
7 Cancer: Adachi
Masako's family and Clan Adachi were a loving group, protective of their ways and those they held dear to them. Combined with Masako's own protective nature of not only those born into her family, but those she chose to bring into it, she and her former clan are able to fit neatly into the Cancer zodiac. It's just a shame that the matriarch of Clan Adachi is the only remaining survivor.
6 Leo: Kikuchi
Although the player never meets a member of the Kikuchi Clan directly, as they were wiped out during the invasion on Komoda Beach, there is enough dialogue surrounding their ways to get a good indication of their defining traits. Sometimes acting like brutes and relishing in the glory of battle, the Kikuchi Clan were seen as a having a fiery personality and were difficult to deal with, but were willing to drop everything and fight for the people when they were called. Their final act of bravery and loyalty makes them fit nicely into the sign of the lion.
5 Virgo: Nagao
The archers of Clan Nagao were not only imaginative individuals and uncompromising in their loyalty to their lord, but also possessed keen analytical and practical skills when planning their attacks, especially with ambush tactics.
This is most evident with Sensei Ishikawa, who teaches Jin not only the ways of the bow, but also how to analyze an enemy encampment to find the best means of attack from the ground. Ishikawa in particular would be a perfect fit for the Virgo zodiac, though he could also fit into several others as his personality is often wild and inconsistent.
4 Libra: Shimura
The diplomatic and fair-minded nature of Libran's fit the Shimura Clan, particularly Lord Shimnura himself, almost perfectly. Holding almost all of the qualities of those born under the Libra zodiac, Shimura fought both physically and politically for his people, not making any special exception when Jin becomes a liability in the eyes of both the Shogunate and the war at large. While some may have called this a callous disregard for his nephew's life, it was more the case of Shimura taking everyone's livelihoods into account, forcing himself to remove his familial attachment to Jin so he could act objectively in the eyes of his people.
3 Scorpio: Kikuchi
Like the Leo zodiac, those who are born under Scorpio are stubborn and brave while maintaining an outward air of passion for everything in life. While many of the clans could be called Scorpian, the ill-fated Kikuchi Clan fits the personality traits most completely, with their willingness to throw themselves into battle for the sake of their people making them some of the bravest soldiers in Ghost of Tsushima.
2 Sagittarius: Yarikawa
Although it would be very easy to associate the zodiac of the archer with the Sagao Clan, the personality traits most commonly found among Sagittarian's more closely suits the Yarikawa clan, particularly the former Lord Yarikawa. His willingness to go rogue for the sake of his clan, as well as his ill-fated attempt to take control over Tsushima from the Shimura clan at any cost, fits him neatly into the Sagittarius zodiac.
1 Capricorn: Adachi
Capricorn's, much like their sci-fi counterparts in Battlestar Galactica, are independent, disciplined, and tenacious, often resulting in them coming in conflict with many people around them simply due to their vastly different personalities. This suits Lady Adachi perfectly, as her willingness to anything to avenge the death of her family consumed her so completely that she and Jin came to near-fatal blows after she proved just how far she was willing to go for revenge.