Hey guys! Can anyone help me find this yaoi/shonen ai. I think it's a part of a collection...

Hey guys! Can anyone help me find this yaoi/shonen ai. I think it's a part of a collection of stories... where the uke suddenly finds a chocolate tin can in his bag and a paper with a message from the seme magically appears. From there they communicate through the chocolate tin can and the seme is actually from the past (around 2-3 years apart). After that the uke finds out that the seme was actually his current best friend once their timeline aligns.