Sure, I understand what it means for Asterion. The MC becomes the first master ever to make this kind of arrangement with him. The Rings tie the two characters together, level the playing field if you will, that allows for new possibilities to move the story along. Just as Luke quipped "you may now kiss the bride", that relationship has deepened and expanded.
But as the author responded to me, there was mention that maybe that scene could be revisited a bit. After all, the MC is a modern man who suddenly gets proof that old gods existed, magic is real, and just downstairs is a snake-man who has a holy mandate to torture his new bovine friend. It would seem that there would be at least some hesitation to change the status quo, even if the personal sacrifice involved wasn't a concern at all.
Anyway I agree with you on the ominous foreshadowing: "hundreds came before, but none were so foolish as to do what you are about to." Seemed like an epitaph. But, I suspect the gods that control fate for this gay furry VN are at least kind.