In season 2 episode 2 of Sekai Ichi Hatsukoi at around 15:31, there's a piano song playing when Takano and Onodera viewed the snow scene.
It sounds familiar, and I just want to make sure.
What is this song?
I think I know which song you're talking about. Looking through the OST for season two helped me. I found out that maybe track 6 is the one you're looking for? It's called, " Shunjun suru Kimochi."
You can check for yourself here.
Although I didn't think that scene has a piano.
But if my suggestion is wrong, the link I provided has the full OST on the playlist. Also, the person's channel has other Sekaiichi Hatsukoi OSTs, you can try your luck there ^^