The mangaka is so clever with the message Yuuji sent to Chihiro. There's nothing saccharine or out of character with it. It's blunt and honest, just like Yuuji. "Let's have another good year" is the answer to Chihiro's question: "you'll forget about me once we graduate right?" Yuuji never thought that, and instead wanted to affirm that their bond ( whether you call it friendship or not) will continue into the future. And future bonds was always something Chihiro could no longer have any faith in since she always moved so much.