If you are looking to explore Japan, the best season is around April as it’s cherry blossom time.
I planned 1 week trip to Japan and covered Kyoto and Osaka.
Here is a short video 
https://www.instagram.com/p/Cp3lkiNOfA0/
Weather: Mild cold but pleasant overall
Hotspots: In Kyoto, i visited Fushimi inari, Aarshiyama, Kyomiji-dera temple and Nishiki Market. In Osaka, i covered Osaka castle, Universal Studio, Umeda Sky Building and Dotonbori.