To start, this is part 4 of 5 for this bow.
You get the original, Relic Bow, in Dynamis.
The FINAL VERSION of this bow after all the upgrades is the Yoichinoyumi.
http://ffxi.allakhazam.com/db/item.html?fitem=8566
Check out mystery tour's website for all the relic weapons: http://mysterytour.web.infoseek.co.jp/ffxi/us/
Look under equipment, then in the left margin under 'Other', click on 'Relic'