Washu is about 20,000 years old, even though she doesn't look a day over twelve. She's the greatest Genius Scientist in the universe, and the 'mother' of Ryouko. See, Ryouko was actually an experiment of Washu's, and was made when Washu combined her egg cells with a creature named mass (as we all learn in ep. #12 of the OVA series.) She created the lovable little Ryo-Ohki the same way, only with a mineral life. Even though Ryouko was an experiment, Washu considers her more of a daughter than any thing else.
Washu generally acts twelve too, you know, creating pseudo space doorways into other demensions, making cyborg versions of herself (Mega Washu) and building a laboritory in Tenchi's house the size of five worlds. You know, all the usual stuff twelve year olds like myself usually do. The only time she doesn't really act twelve is in episode #8 of the OVA series, when she offers to bear Tenchi's child... (!) She even uses looking twelve to get out of work.
Washu's only about four or five feet tall, so she always wants everybody to call her 'Little Washu'/'Washu-chan'. She has light green eyes and pointy bright pink hair. I think I think her hair's a little weird, because sometimes her hair is so long about the last four inches of it drag on the floor, and other times when she has it tied up it looks to only be a foot or two long. But, who am I to question such things? After all, Washu is a goddess. (No that's not a figure of speech, she really is one.)
Of course, who Washu is in the Tenchi Universe series is slightly different, but she still is the greatest genius in the universe who's I/Q cannot be measured and who built her lab which is the size of five worlds in tenchi's space under the stairs and all that, but in this series there is nothing about her being the sister of Tsunami and Tokimi or any of that, and she was the deamon who was imprisoned in the cave for seven hundred years, not Ryoko like in the original OVA series.
In the second OVA series, you learn that Washu was married once 20,000 years ago, and had a child, a baby boy, who had light curly blond hair and green eyes just like hers. Her husband was a student at the royal space academy, and she loved him very much.
But he was from a very distinguished family, and while she was away messengers came from his family and took he and the baby away. She never saw them again.
As I already told you, Washu is a goddess. She's supposed to be I think the sister of bolth Tokimi and Tsunami, but she doesn't look a thing like either one of them.
She developed amnesia a long time ago and forgot that she was a goddess, which explains her genius and 'super powers' for one thing. Her sister Tsunami is pretty normal, but you can't really tell if Tokimi is good or bad. Oh well.
Being a goddess, she has relitavly magical powers and since she is the 'mother' of Ryouko, she is psychicly connected to bolth her and Ryo-Ohki, only her connection to Ryo-Ohki is much weaker.
Washu has a sence of style all her own, and doesn't dress like any of the other charecters. She's zany and fun, and I think the funniest of all the charecters, also the most interesting, because there's a lot that isn't really known about her.
One thing for sure though, she has a bit of an ego, as is demonstrated by her little Washu A and Washu B puppets that are on her shoulders a lot of the time in the Tenchi Univese series praising and complementing her, being very much the little yes men, er, women. "Washu, you are a genius!" "The greatest in the universe!" Oh boy. (Kinda wish I had some o' those, actually...)
She (in my opinion) gets the best lines in the series. For example, when she creates a teleportion device to get them onto the space ship where Ayeka, Sasami, and Ryoko are being held in Tenchi Universe (Space I):
TENCHI: If it's a teleporter, why didn't you let us use it before??
WASHU: Because it's range is only 800 metres. IT DOESN'T WORK LIKE IT WOULD IN A CARTOON!!
(Hee hee!) I love it.