Train transport from Karuizawa to Osaka

I finished my hiking in Karuizawa and would like to fly out from Osaka. It will be great if I can train the journey in one day. If not possible I am happy to stay overnight in Nagoya. Please advise. Cheers

I am not sure I understand the question. If it's for "today" (March 6th), I guess it's too late. But if it's tomorrow, by shinkansen, Karuizawa to Tokyo is 1 hour, and Tokyo to Osaka is 2.5 hours. Provided there are no suspension of trains or significant delays, you should be able to catch a flight in Osaka in the afternoon. Also, why Nagoya?

Karuizawa to Osaka via Tokyo is a couple of hours. Three trains - one to Tokyo, one to Shin-Osaka, and one to Kansai International. It is simple/not hard and might be less than five hours. If you visit Japan and understand how quick the shinkansen network is, thinking it takes more than a day is weird.

Yes, you can travel from Karuizawa to Osaka in one day by train the fastest routes take about 4–5 hours with the help of 2–3 transfers. If you have more time the i will suggest staying overnight in Nagoya is a convenient option. or take help on vacation otrips to reduce the burden of your travel.