I have an upcoming JAL itinerary that starts with a codeshare on Alaska Airlines metal to SEA then JAL to NRT and JAL to Osaka ITM.
Will my checked bag be sent all the way through or will I need to pick it up at either SEA or NRT?

I also booked a domestic flight on a Sakitoku fare but it now makes more sense for me to take an earlier flight. It is currently within 54 days of departure so I was wondering if there's any option of a same day change to an earlier flight or something. A dinner opportunity came up but it's not worth losing 50% of the fare over. If only I had booked at least Tokubin...