This is the version of Kimi ga Ita Kisetsu Which was updated with the latest patch and DLC which includes Kazama Touko and Munakata Misae character routes, as well as updates some CGs to remove tracing. It also includes Muv-Luv Alternative Chronicles: Confessions as a bonus story.
Also, this version was updated to not require a separate installer: the game will install itself upon the first launch of KimiIta.exe and will start as normal on subsequent launches. Due to how it works, your antivirus may trigger a false positive. It also includes the Universal rUGP Win10 crash fix (https://vndb.org/r94522).

Difference from the version in https://sukebei.nyaa.si/view/3211792 : includes all updates and DLC, portable. Yes, the 20th Box version only includes the base game.

VNDB Links:
Kimi ga Ita Kisetsu/君がいた季節 https://vndb.org/v443
Muv-Luv Alternative Chronicles: Confessions/マブラヴ オルタネイティヴ クロニクルズ 告白 https://vndb.org/v32795