In the past, entering Japan during a connection required payment of additional taxes and fees that would not be included in your ticket price. Once I entered (on a USA passport so there were no visa issues) to use a landside lounge and was forced to pay IIRC 3000 yen in cash before I could go through exit passport control. Check carefully about the rules before entering Japan on a connecting ticket.

If MNL to SEA is DL, you'll be in NRT T1 in an area that DL has been increasingly leaving, so I'm not sure whether some of the shops have also closed. It might look like an abandoned ghost town. There was a publications store toward the DL gates that I always liked. Around the area where originating passengers enter airside after passport control and security, there were a lot of luxury good stores and some duty free places offering alcohol samples (plus perfume and tobacco), so the retail outlets you want are likely to be closer to the gates. Depending on how much time you have, you can walk airside (past those luxury stores) to the area used by *A carriers, which might have more to offer currently.

HND will be the international terminal, which I hate and consider to be inferior for airside shopping compared to NRT T1.