I went to JR office and they can only give me the ticket from Shinjuku to Otsuki I have a reserved seat from Shinjuku to Otsuki That seems to be a mistake.
The train which you plan to take is Rapid Fujisan for Kawaguchiko, which is an extra train scheduled to run only on Fridays until the 3rd of March 2017.
JR-Fujikyu through reserved-seat tickets of this train are available at counters in JR Ticket Offices of East Japan Railway Company [JR-East].
Seats of this train cannot be reserved separately for a Fujikyu section.
So, in order to have a reserved seat until Kawaguchiko Station, you need a JR-Fujikyu through reserved-seat ticket.
Please inform JR-East of this mistake then exchange your current ticket for a correct one.
(There are a few JR-Fujikyu through train services named after Mount Fuji, so please say "Rapid Fujisan" clearly for distinction.)
If you have paid 520 yen for your current ticket, the ticket is a JR reserved-seat ticket; if you have paid 1840 yen, the ticket should work both as a JR basic-fare ticket and as a JR reserved-seat ticket.
For the JR and Fujikyu basic fares, you can use a Suica or PASMO card, in which case you don’t need a basic-fare ticket.
- A blog article in Japanese written by a railroad fan:
http://s.webry.info/sp/tomodachiya0221.at.webry.info/201607/article_1.html
: In the last photo, you see a pale blue reserved-seat ticket of Rapid Fujisan for a ride from Shinjuku to Kawaguchiko, which was issued by JR-East.
- Fujikyuko: Introduction in Japanese of Rapid Fujisan:
http://www.fujikyu-railway.jp/train/kaisoku_fujisan_2016.php