I'm pretty sure that's from For My Dear....

誰もがキズを持って
いるから時に優しさが
しみてきて　とても痛くって
泣き出しそうになったりする

Dare-mo-ga kizu-wo motte
Iru kara toki-ni yasashisa-ga
Shimite kite Totemo itakutte
Naki-dashisou-ni nattari suru

Because everyone bears wounds,
It’ll sometimes hurt so much
For kindness to sink in,
That we’ll feel like we’re going to cry.


What you're thinking of is the 時に優しさがしみてきて toki-ni yasashisa-ga shimite kite part.