Koyasan World Heritage Ticket from Kyoto

I am visiting Koyasan for one night from Osaka but going onward to Kyoto. Do I buy a Koyasan World Heritage Ticket? It seems that ticket is best for a trip to Koyasan if you are returning to Osaka. Or should my onward journey to Kyoto include a slight detour to Osaka before going onward to Kyoto so I use the return aspect of my ticket? I don't mind if my journey is slightly longer in distance and time, but wouldn't do so if the saving was not worthwhile. Thank you.

You can buy nankai railway 1 day pass
This pass valid koyasan by nankai railway
As nankai has no rail line in kyoto
So you can buy 1 way ticket to reach kyoto
JR namba, JR shin imamiya,JR wakayamashi rail st has connection with nankai railway

Or should my onward journey to Kyoto include a slight detour to Osaka before going onward to Kyoto so I use the return aspect of my ticket?

If you use googlemap to search your way by public tansport from Koyasan to Kyoto, you will find it goes through Namba. It is not a detour at all. You should specify the exact place you will go in Kyoto. You can use JR, Hankyu or Keihan depending on the place in Kyoto.

You might check Koyasan World Heritage Digital Ticket

https://www.howto-osaka.com/en/ticket/koyasan/

Which is somewhat cheper

There is a direct Highway Bus Service from Koyasan to Kyoto, which costs 2,800 yen per person.
It departs from Koya Police Station Bus Stop at 15:27 and arrives at 18:35 in Kyoto.
I recommend to book this bus service as below:

https://idou.me/search/bus/wakayama-koyasan/kyoto-kyoto/20250416