Keikyu line to Shinagawa
Keikyu trains reach Shinagawa in around 15 to 20 minutes. Pay with an IC card like Suica or Pasmo, no reservation needed.
Rush hour trains get very crowded. With large bags, avoid 7:30 to 9:30 on weekdays if you can.
Tokyo Monorail
The monorail runs to Hamamatsucho, where you can change to JR lines. It is covered by the Japan Rail Pass, but needs one more transfer than Keikyu.
At Shinagawa
The Shinkansen gates are inside the JR area. Use the elevators and allow 10 minutes to reach the platform with big bags.
With a Japan Rail Pass, seats with an oversized baggage area are included at no extra cost. Book them by scanning the QR code on your pass at a Shinkansen ticket machine or at any staffed JR desk. Get your Japan Rail Pass