'Fulfill' in the Bible

So I thought to myself I ought to tell you that you must make a public purchase of this before the town residents and the elders of my people. So if you intend to act as the related redeemer, then do so. But if not, let me know, because except for you and I after you there is no one to fulfill the duties of a related redeemer." The man responded, "I will act as related redeemer."