You may be able to glean something of Ra’s romantic history from actual mythology, though that doesn’t necessarily apply to Dr. Washington also.
I can’t get over the classic comic idea that the first time Tachyon and Unity met one of them threw their arms around the other and kissed their partner, confusion reins and the one says “Oops! Wrong time period” and jumps on to the future/present day for them. Then the first time they met ‘for reals’ the kissed becomes the kissie and they can both claim
“The first time we met, she kissed me, we hadn’t even been introduced”
(you know, because a tech wizard and someone who breaks the lightspeed barrier can both time travel if they put their mind to it!)
Yes. We need steampunk alt versions of Tachyon and Unity for just this scenario. 
Just because I’m watching this spiral out of control, and I do hate to rain on everyone’s parade: Tachyon and Unity are absolutely NOT romantically involved.
Tachyon had already been married for years by the time she invited Unity to come work for her lab. They butted heads at first, due to their differing ways of approaching issues and Tachyon’s love for order vs. Unity’s love for “just doing things” and not having a thought-out process. Eventually, they became good friends, understanding and respecting each other’s differences and working well together, both in the lab and on the battlefield.
Sorry to be a stick in the mud for your ideas, but I hate seeing so much attention being paid towards a path which will ultimately lead to disappointment.
In exchange for my nay-saying ways, I give you the name of Tachyon’s wife: Dana Bertrand
Enjoy!
Haha! Trick successful, knew I could get the name out of you somehow!
Well, maybe not but we got a name!
Man, I know this is all wrong, and yet I still love it! So cute!
Ha! Christopher, you are awesome. Looking forward to learning more. 
Ironically, this is going to affect a friend’s fanfic villain whose main motivation is to pair up the heroes with each other- by any means necessary.
Prepare… for a match made in HELL!!
Or more Eugeneticly motivated? Some kind of creepy organisation that tries to make specific heroes fall in love with each other (endangering many bystanders in the process) as to create THE ULTIMATE HERO BABY (OK, I stole this from the plot of a certain rhythm game).
No no, nothing so forward thinking, just an insane rabid fangirl with superpowers to back up the madness. I won’t go into more detail than that, though. All the crazy pairings are slash and/or massively out of character, which is part of the point.
I won’t say any more about the character here though, since I think it would run afoul of the no talking about hero concepts rules.
We have a running joke that Ra and Citizen Dawn have a thing. Both harness the sun, yeah, but the whole “taken within the sun” and stuff, we all thought that would make sense.
On a similar topic, has anyone noticed Citizen dawn looks like the sister of Tachyon?