This is a fantastic fare. Thank you to the OP and others who have posted. I am having issues with i class availability appearing available in ITA Matrix, but google flights doesn't find it and a travel agent thought there might be a point of sale restriction to have the ticket issued in Korea. In ITA Matrix, I tested changing the point of sale to USA and still saw the appropriate fare so I'm not sure that's the issue.
Google flights and the agent only found C fare class on the outbound.

Any other ideas on what to try? I'm targeting January 2 or January 3 so wonder if JAL is holding back i and d fare class for the holiday period. Although I don't know why ITA Matrix would show availability. (SEL-TYO in Y and TYO-ORD in i)

Overall itinerary:
SEL-ORD
ORD-EZE
EZE-ORD
ORD-SEL

Cheers!