The following worlds are where you may obtain Blood Rubies from defeating enemies:
Grayvale
Tyesuc
Barabas Castle
Bloodfang Palace
Hellfire Plains
Requiem Woods
The following worlds are where you may obtain Gen from defeating enemies:
Coria
Eidos
Lenais
North Point
Aerris
Terrus
Obsidian Peaks
Metalos
Vanguard
Velos
Aeramus
Entvine Forest
Mermos Islands
Senai'Ka
Sol Ville
Zion
Glacius
Jelduno
Veritas
Atlantis
Eden
Aisu
Canan's Plateau
Ruins of Syn
The currency exchange for Gen>Blood Ruby/Blood Ruby>Gen is as follows: Every 1 Blood Ruby equals 2 Gen. So in other words, if you earn 10 Blood Rubies, it transfers over to 20 Gen if you enter a world where that is the chosen currency. If there are any questions or concerns, feel free to PM me and ask me! ^_^