Under the Miracle Cherry Tree

The main lead dies and returns again not having aged a day old from when they left. The leads try and figure out what happened leading up to their death and try to fix what they can.

Both follow a group of high school best friends who are impacted by a tragedy. Through past (high school) and present (adult) timelines, a supernatural "time-slip" reunites them as they try to fix the past and prevent their biggest regrets.
Additionally, both are set in Nagano Prefecture: Orange in Matsumoto and Boku Dake ga 17-sai no Sekai de in and around Lake Suwa.
Plus, Yamazaki Kento appears in both (but just a guest role in 17-sai)!

They're group of childhood friend and there's some case of love between them. One of them died at young age and that makes the group separated into their own ways. 7 years later teir died friends come back and her come back reunited the group.

Both dramas start with two classmates falling in love and one of them tragically dying and mysteriously back to life, making them experience what could have been and ultimately coming to terms with everything and being able to let go.

Differences:
Eien no Kinou is a BL.
In Boku Dake ga 17sai no Sekai de, there is a time skip of several years, before the decaesed comes back.

I believe both has the same vibe. The plot is different but the feeling is pretty much the same.