Commander Shepard of System Alliance is unique. Even amongst other humans and aliens. It's not just about what they have achieved and accomplished over their years of service in the military.
The first unique thing about them is their ability to switch gender. Yes, from male to female and vice versa. But unlike some of her relatives, who's can change gender whenever they liked, Jane Shepard has to be doused in either cold or hot water to change their gender.
It's actually unknown what the initial gender of commander Shepard actually is. When their ability is discovered by System Alliance, some research has been conducted, mostly by the LGBT community, to study her ability. But when their research reached to the point of abduction, one of her relatives, who is said to be the matriarch of their family, destroyed the research facility by unknown means.
Their ability to switch gender is not known to Council and other alien races, until they had their Eden Prime mission, when Nihlus Kyrik, Spectre that accompanied commander Shepard, witnessed the transformation of male, black-haired John Shepard to red-haired, female Jane Shepard. He is apparently so shocked that he survived a shot to the back of his head later that day.
Speaking about uniqueness, their family, and its branching line are certainly that. First let's talk about the matriarch of the family, Ranma. She, like commander Shepard, can switch gender, but without the use of hot and cold water. She can turn into a handsome pigtailed, black-haired male but rarely does so.
She is also strong, extremely so. Those that once served together or under commander Shepard has said that they were really strong, able to send guys flying from their punch, but Ranma's strength eclipsed commander Shepard with a very wide margin, taking their punch that usually send their opponents flying with just one finger when she visited Shepard once.
But her main strength is her technique and speed which seem unreal. She can punch over 800 times in just 5 seconds, cut steel using what seems to be a blade of air, encased something or someone into a block of ice, create a tornado, and many other superhuman feats. That's not including her possessions that defied the law of physic and reality like her stave and spear. Many scientists, mainly salarians, have tried to explain how she can do all the stuff she showed when she visited Citadel after First Contact War.
Under her, there are two main lineages. One is Yagami. The other is Yukihira, with few branching families from both lines.
Not many facts are known about Yagami, other than those from Yagami's line is a usually skillful fighter that can produce a purple flame of unknown origin to fight with. But even though they're powerful, they rarely are in the spotlight, and thus, not many things are known about them.
If Yagami's line is a fighter, then Yukihira is the support. Those in the Yukihira line is a genius in the craft of cooking. They tend to be chefs, patisseries, or involved in other cooking-related stuff.
Excerpt from Mordin Solus's observation when the Normandy's crew visited commander Shepard's grandparents.
It appeared that any woman born in the main family or branching one will always have bright red hair, sometimes with a different shade of red. While the male one will have black hair. One peculiarity I've seen with their hair is they grow extremely fast.
Any member of the family also seems to have an extended lifespan and resistance to sickness.
About the matriarch, Ranma, rumors have it that she is immortal, untouched by age. I have seen the pictures of her from 300 years ago, and she certainly doesn't seem to change or aged at all.
Also, the commander her/himself apparently learned her superb culinary skills from her/his grandfather who's worked as a chef.