I will be going to Japan in late March/early April and would like to experience a beautiful outdoor Onsen that looks over the ocean. Time wise it has to be in or around Miyahima/Hiroshima or somewhere back to Tokyo. Any suggestions?

There aren't very many real onsen in the Hiroshima area. Not sure if it matters to you but the water there is the Inland Sea, not open ocean (so there may be land in your view).

I think emd found a nice rotenburo with a view of water. Might have been in Aichi prefecture, in Ise, or maybe Shizuoka.

I can suggest looking in the area of Atami Onsen and the Ito peninsula. That is a likely area for what you want. It is south/southwest of Tokyo not far from Fuji-san.

http://www.jnto.go.jp/eng/location/interests/hot.html

Oops, I mean Izu Peninsula. Ito has an onsen. At the above link take a look at Higashi Izu and Nishi Izu, in particular.
(higashi=east, nishi=west)

Try here:
http://www.japaneseguesthouses.com/d...uoka/index.htm

Inatori Tokai is a ryokan hotel with rotenburo (outdoor baths) that have ocean views. It is in Higashi Izu, which apparently is a town. This kind of place would very likely allow the general public to use the baths for a fee (without staying overnight).

We once stayed at this Imaiso onsen ryokan, in Izu (near Tokyo), and it's right on the ocean, with open-air onsen. It's rather expensive, but was nice--homepage below. It was many years ago, so things may have changed, though. They speak English. There are many nice onsens in the Izu peninsula, and you can take "Romance car" trains from Shinjuku station.
http://www.tokaikanko.co.jp/english/imai/