Koyama Clan

The Koyama Clan is an infamous clan specializing in Taijutsu, hailing from Kumogakure. They are a family filled with trained assassins with the trait called Ice Blue Eyes which mainly occur in the men born to this family.

Background
Founded by a man going by the name of Aoshi, who was a leader of a group of trained assassins specializing in both Ninjutsu and Taijutsu. Not much is known, other than the fact that he originally had Ice Blue Eyes.

To determine the head of the family, the eldest son of the family is automatically put the position, unless they are dead or killed in battle, or if they choose to retire. If they do not have a child or if their child is presumed dead, then their younger brother or their nephew will take over as the heir. Typically, since nearly all of the heads of the family have been men, there's rarely any women who take over as head of the family. It's been documented that only three women headed the family, the most recent heir being Sumire Koyama.

Ice Blue Eyes
Considered as a Kekkei Genkai that mainly runs through the men of the family. Characterized as "eyes as light and cold as ice", mainly men are born with this trait, while the women are born with regular blue eyes. There's a 1 in 5 chance that a woman will be born with these eyes, however if they are born with these eyes, they will be forced into doing training like the men do, compared to having to have the decision of doing assassinations or not.

Members born with these can unlock a stronger, deadlier side of them, that was said originated from the founder. Depending on the user, they are activated by various means, depending on their mental state. However, there's a possibility of them activating it at will, but they needed intense training to fully train it.

Once activated, it forces the user into a sadistic, heartless killer, who wouldn't stop and have mercy on people. This allows their strength, speed, and chakra to slowly increase, but because of this power, there's a lot of cons that goes along with this.

Without the proper training, the user will become severely exhausted, possibly to the point of going to a coma if they overuse it. To fully master it, strict training is usually forced upon them at a young age, to prepare themselves properly.

Also, the kekkei genkai gets deactivated when the user's vision is blocked and their bodies are restrained, however, it can be useful when preserving chakra. This forces their mental state to focus and cool off, which quickly switches them out of their other state, and calms them down.

Summoning
The Koyama family has four summons that have been in their family for generations, however, usually the heir must make a contract with the children of the summons of their fathers, while the other members are allowed to use the head of the family's summon.

The summons are a peacock, a komodo dragon, a white tiger, and a tortoise, which they are named after the four cardinal beasts. Each of them specializes in a different ability, which allows them to be summon individually (or together, just depends) to aid the user. It's possible for the children to summon them without a contract, if they're in danger, using a special jewel that's granted to them by their parents. They can't choose which summon, however, and if all the summons are already in use, it will automatically summon a member of the family to help them.

Suzaku, the crimson peacock, can transform into various types of birds, and mainly is useful for aerial searching. Seiyuu, the komodo dragon, can spit venom that can burn the ground, mainly used as a way of distraction. Byakko, the white tiger, can be useful for mainly fighting and ground transportation, specializes in taijutsu. Genbu, the black tortoise, specializes in mainly healing, though, he cannot heal more than what he's trained to do.