This drama is about two men and two women who are reunited at the 25th anniversary class reunion of their middle school in Nakano, Tokyo.
"A person falls in love three times" is the sub-header. It's going to be about 40-year old men and women looking back their lives so far and trying to reset them with their "true" loves.

At first, this drama reminded me of another drama, "Dousoukai" that was broadcasted in 2010. However, "Dousousei" has a different feel with more focus on one's third love.
The original story of Dousousei is a 2011-2012 manga by Saimon Fumi. Saimon Fumi wrote/drew Tokyo Love Story (manga) which became a big-hit TV drama in 1991.