Heritage
Very little, almost nothing, is known about Su's background. The only slightly substantial information we are given is that it's a warm place and it's not India. Other than that, no one really knows where Kaolla Su and her family are from. And maybe they want to keep it that way. But I'll try to examine their lifestyle just the same ^^

One of the most noticeable things from Su's country is the clothing that is worn. Su and Amalla both wear sleeveless, midriff-bearing tops which are presumably made of a light material. These are paired off with long and flowing skirts that would most likely also be made of light material. Tassels of some sort are used to decorate the outfits, and the colours are always very bright and vibrant. Any type of jewelry or accessories, such as necklaces, armbands, bracelets, anklets, and hair clips, are probably made of gold, and a triangle pattern trims the outfits on both Amalla and Ranba's clothing. Neither socks nor shoes are ever worn by the women or the men. These outfits may be a little revealing, but they are very pretty at the least and would be essential if the weather was hot or humid.

The men's clothing also appears to aim to be as light and comfortable as possible. The shirts begin below the shoulder and the short sleeves are slit, possibly for comfort and easier movement. A red length of material serves as a belt and the pants are secured just below the knee. The triangle trim appears a lot in Ranba's outfit. The colours aren't as bright as that of the woman's, but perhaps they're supposed to be more "manly" colours? He also wears some jewelry consisting of gold earrings, a thick gold band around his neck, and two anklets on each ankle.
I'm not a great fan of the wedding ceremony outfits. They were very form-fitting and looked slightly cheesy. The groom's outfit seemed especially stereotypical >.<. Then again, I'm not even sure they're part of Su's culture. For all I know it might just be one of Mitsune's creations for another one of her failed plans!
The third eye appears on many of Su's inventions and is ubiquitous when it comes to her culture. Emblazoned on the front of the street car Ranba arrived in was a pair of elephants, each with a third eye. Their currency boasts an elephant with the three eyes, and in the wedding ceremonial hall had a huge sun with the third eye at the center of attention. Su has a red dot on her forehead, I believe, that is basically supposed to be the "third eye". I think it has to do with their religion, but maybe it's just a custom from their country, or even a marking to show their ranking.
Food isn't mentioned very much in the series, but in Episode 2 Su apparently cooked for the residents of Hinata Inn. All the food was swimming in some sort of red sauce that was presumably spicy! Needless to say, Naru, Keitaro, and Mitsune were running for water after a taste of the food. So spices are an essential garnish to every meal in Su's country!
All of the Su/Ru siblings are very athletic, lithe, and strong. They can all jump around wherever they please with no problem, their defensive and offensive skills are excellent, and they could probably run long distances without a problem. If everyone from their country possesses the same stamina, methinks you wouldn't want to be their enemy. I think that if they wanted to be professional assassins, all three of them could pull it off with ease, especially Ranba. And Su... well she could if she was a little more quiet and discreet during her attacks...
But they're not all physical force. All three are very in tune with nature, and so I assume most of the people of their culture might be as well. Both Amalla and Su decorate their rooms with various wildlife that's remniscent of a jungle, probably to ease the homesickness. They all communicate with animals to some extent and use natural forces as their weapons. Concentrating on the animal aspect for now, both Su and Amalla make use of their bond with animals for protection and offensive battle. Ranba, however, uses his communication with animals to calm them, stop their destructive behaviour, or disarm them. Amalla uses her pet white alligator "Whitey" as a bodyguard of some sort. He attacks whomever she orders him to attack and is quite effective at scaring the perpetrator. Su makes use of Tama-chan of course! She seems to have the ability to make Tama-chan multiply and she sends hoards and hoards of flying turtles at her opponent. Ranba sticks with simple white mist that seems to wreak havoc on anything in his way within seconds.
Not only do they use animals in battle, the Su sisters also use musical instruments to give them a bit of control over the elements. Amalla utilizes a flute while Kaolla sticks to a guitar/mandolin. One of the main elements they can control and manipulate with their instruments is the weather.
Their country also appears to enforce a strict honour system, much like any country with royalty would. This is demonstrated by Amalla since she refers to her brother by his title and bows to him when in his presence. Although she herself is considered royalty, Ranba is of higher ranking than she is, so she must treat him as any regular citizen of her country would. Of course we wouldn't see Su having any use for these rules and protocols ^.^;;

One thing we do learn about Su's culture (from the anime) is that they have a very serious view of responsibility and growing up. Everyone has a duty and is bound to their duty, whether or not they are of high status. Ranba revealed that he had been in the army for two years and was joining it again for a third year. Even though he was a prince he couldn't shirk this responsibility. From this information we know that Su originates from a war torn country, or maybe one that is on the verge of war.
There is no specified age to separate adults from children. According to Ranba a person becomes an adult of their own will. And sometimes that change from childhood to adulthood might be forced upon a youngster under specific circumstances. It's not based on your age, but on your willingness to take and handle responsibility. And once you've shouldered that responsibility there's no turning back. In their country the outlook of life seems to be "Whatever you have, whatever the situation, it's what you have to live with. You can't change it. No one is an exception, everyone is the same, and there's nothing you can do about it. It's your duty."
Su's country, which will probably forever remain unknown, has many great things about it as well as not-so-great things. Although she's run away to Japan because of her country's protocols, rules, and expectations, she really does love her country. In fact, she fully intends to go back and further it's technology for the better someday. With Su-chan at the helm, the country will become an interesting mix of technology and nature, ne?
<< done eating! want more~