One way JT ticket

Hi , I will be travelling to Osaka / Kyoto and Tokyo in Nov 18. As I will be travelling within the cities, I find that it is not economical to buy the 7 days JR pass but will be using the suica card for local transport within each of the cities.

However, I will need to buy the following one way JR ticket. I have searched JR West and JR east websites but it looks like they do not sell one way tickets in advance on their websites.

1. Can someone please let me know where I can buy these one way tickets or exchange vouchers in advance before I arrive in Japan?

2. If advance booking outside Japan is not available , do I buy the 1 way tickets when I arrive at the JR stations in Japan? Can I buy them before the actual date of departure at Kansai International airport?

3. As it's the peak season, will there be limited seats for each journey? i.e. if I don't buy in advance before I arrive in japan, will there still be tickets available when I buy just before the departure date?

4. These are the one way tickets that we will need:
(a) From Kyoto to Hakone. Preferably with seats (unreserved or reserved seats) as it's a long distance journey.
Note: I will buy the Odakyu limited express ticket for the journey from Hakone to Shinjuku

(b) From Tokyo to Nikko and return to Tokyo

I'll be very grateful for the advice. Thank You very much.

Ju

What time will you arrive at KIX?
From which airport do you plan to leave Japan?
How many days are you traveling?

You can not purchase it before entering Japan.
You should ask and purchase "JR-WEST" counter at KIX.
https://youtu.be/g22kvpL_Syw
At JR 's counter you can not purchase tickets for the Odakyu Line.

Purchase at the counter for one way ticket. Most trains are not far apart so you shouldnt be waiting long for the next train when you get your ticket.

Kyoto to ODAWARA is what you are after. If you are going to Hakone.

You can buy it at any JR ticket window or service counter. From 10am 30 days out.

If you want a guaranteed seat, then you need to by a reserved seat.

You can try a un-reserved seat, but it the train it full, you'll be standing. And since most trains start at Okayama or Shin-Osaka, getting a seat in peak travel periods from Kyoto might be difficult.

You may want to check "SmartEX", a service provided by JR Central which operates Shinkansen from Shin-Osaka to Tokyo.

https://smart-ex.jp/en/