Where are the Bleachers in Tokyo Dome?

Without seeing the tickets I can't really say, but those sould like standing-only tickets. Enter through the gate number written on the ticket, head up to the level number also on the ticket, and try and jostle for a good position in the very back behind the seats.

I've only been to Tokyo Dome a few times, and I haven't had the pleasure of mixing it with the hilariously rowdy fans in the standing section, so I hope someone else can give you a more helpful answer.

Nevertheless, Giants vs. Dragons should be a scintillating game.

Bleacher seats in Japanese are usually called 外野自由席 (gaiya-jiyuuseki) - which means outfield general admission. According to the Tokyo Dome website, the 1,000 yen tickets are actually 立ち見 (tachimi) - standing room only.

So you most likely won't be "sitting" in any section.

So then is there a special "standing" area like there are at certain soccer stadiums in Japan (Todoroki, Komaba, etc.), or are fans just supposed to stand behind the seats in the concourse area?

I recently bought some tickets from e+ for a game at Tokyo Dome, and while they have a chart saying how much the S, A, B, C, and D tickets are, and a map of Tokyo Dome, they don't say where the sections are on the map.

So I had to find the Tokyo Dome website in a different tab, and there I found this seating chart, complete with legend. (Now, why can't e+ use that page? It's a lot more useful that what they've got.) The yellow section on this seating chart is for tachimi.

And, yes, it's basically in the concourse. I've "sat" there a couple of times, after getting tickets from a friend who subscribes to one of Yomiuri's newspapers. (They give away free tachimi tickets to try to get people to subscribe. 10 years ago, a tachimi ticket would have been considered a great prize.) Many people bring mats to sit on, although depending on your height, there may be a bar blocking your view sitting on the ground. Some people would bring small folding chairs (the ones not even knee high), although I'm not sure if that would still be allowed with the heightened security at public events.

Nonetheless, please enjoy the game.

I will definitely enjoy the game. Hopefully my parents will, too. Are the "tachimi" rows individually raised, with crush barriers separating the levels?

Here's an example of what I'm describing. See the lower level of the stadium in this photo: