According to the questing guide, there is already a specified quest to this item....
For a Rudra Bow:
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1 Gakkung [2] [1/1] DONE!!
3 Hand of God [3/3] DONE!!
5 2 Carat Diamond [5/5] DONE!!
10 Muscovite [0/10]
25 Pearls [25/25] DONE!!
50 Oridecon [50/50] DONE!!
100 Holy Water (unnamed) [0/100]
250 Fake Angel Wing [01/250]
500 Immaterial Arrows [500/500] DONE!!
1,000,000 Zeny [1,000,000/1,000,000] DONE!!
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IGN : wasabi/eMCee
That's pretty easy for the hardest bow to get in-game...only one of those items is MVP-dropped, and it's by Osirus, who's in the MVP room... <_<
this quest has been completed