When you exit from the custom gate, go down any nearby stairs to the basement, B1F floor, of the airport building.
Please buy a train ticket from Haneda to Mishima Station via Shinagawa Station by Shinkansen Kodama super-express. The price is around 4500 Yen without seat reservation, and 5000 Yen with seat reservation. (No reservation is needed, you can find a seat.)
You can show the following Japanese text to the person.
You can also buy a round ticket, but there is no discount.
To Shinagawa Station, there are two ways: Keikyu train or Haneda Monorail. Keikyu is easier, for it directly goes to Shinagawa. The monorail goes to Hamamatsu-cho Station, and you need to change trains to JR Yamanote-Line to reach Shinagawa (a few stations away).
To have fun, however, the monorail is better because its view is much nicer (it is like a roller coaster when you take a front seat).
The time to Shinagawa is around 30 minutes in both ways.
In Japan, you have to keep your ticket until you get off. When you insert a ticket to a control gate, it will pop out on the other side. Please take and keep it during your travel. If you lose it, you have to pay again.
The Shinagawa Station is big, with over 10 platforms, each dedicated to a specific line. The Shinkansen platforms are tracks #21-24. Please go across the whole station as follows. It takes 5 minutes.
Please take trains to West-bound, i.e., Osaka and Kyoto direction. There are three types: Kodama, Hikari, and Nozomi. Nozomi is by far the most, leaving every 10 minutes. You need to take Kodama, though. It leaves every 30 minutes and stops at all stations.
Without seat reservation, you must ride on cars 1 - 7 or 13-15. Please check the car numbers on the platform and queue in the waiting line. (In Japan people always make a queue.)
From Shinagawa, Mishima is the 5th Station (Shinagawa, Shin-Yokohama, Odawara, Atami, Mishima), and it takes about 50 minutes.
Again, do NOT take a Hikari or Nozomi Shinkansen. Well, a few Hikari stops at Mishima, but when you take a wrong Hikari, it usually goes much farther and risky.
There are 2 exits at Mishima Station (North Exit - which you will encounter soon as you come down the stairs and facing the outside the building. ) Please do not exit from North Exit.
You have to go to the South Exit. You go a long way through the underpass before reaching the south gate (5 min). Not user-friendly, but there are sign boards for directions.