Getting to Hiroshima from Haneda airport?

Hi everybody! Me and my girlfriend are arriving in Haneda airport on july 12 at 03:00 pm, and we would like to travel directly from there to Hiroshima. Some research suggests we take a bus to Shin Yokohama station and there take the shinkansen to Hiroshima. Is this a good idea? We do have JR passes, can we activate them there? How do we go about this? Or is there an easier alternative to getting to hiroshima we haven't discovered yet? Arigatou in advance guys :)

I recommend to take a Keikyu train to Shinagawa and then the shinkansen to Hiroshima. The Japan Rail Pass can be exchanged at Haneda Airport between 7:45 and 18:30 or at Shinagawa between 9:00 and 19:00. Indeed, Shin-Yokohama has the earlier opening hours for exchanging the pass in case you arrive at Haneda very early (open from 5:30 to 22:30).

Here is a complete list of exchange offices:
http://www.japanrailpass.net/en/exchange.html

Thanks for the info! I�fve done some extra research and it seems that Shinagawa station is indeed the best option. Do you maybe have some additional information on how to go about this? Can we catch a train to Shinagawa straight from Haneda airport? Do we need to reserve a seat on the shinkansen in advance? Will it be easy to see how/when/where we need to transfer in Osaka? It�fs our first time in Japan and we�fre a bit nervous about finding our way around the railway network :). Thanks in advance, good karma coming your way!

Can we catch a train to Shinagawa straight from Haneda airport?

Yes, Hyperdia is your friend.

Do we need to reserve a seat on the shinkansen in advance?

If by "in advance" you mean "before arriving to Japan", then it's nether necessary nor possible. In fact, reservation is never necessary on the Tokaido/Sanyo/Kyushu Shinkansen, but if you want to make one you can do it at either Haneda or Shinagawa.

Will it be easy to see how/when/where we need to transfer in Osaka?

Yes, just follow the signs.