Marco is featured in Chimera's very sad past, from the flashback in episode 72.

Chimera's actual name is Eileen. Years prior to the 2nd War, she met and saved Marco, a man of the then-dispersed Chess Pieces. The two eventually fell in love with each other and one day, held their wedding in a small church. However, in the middle of the ceremony tragedy befell: when Eileen and Marco finished exchanging wedding vows and rings and were about to kiss, they were interrupted by a hostile group of villagers. The mob, who were Chess victims still living in vestiges of the war, were on a witch-hunt for the Chess and knowing Marco's former affiliation, took him captive. For she loved him despite this, Eileen desperately beseeched for her fiancé's life, protesting Marco had already defected from his organization, and that the war was already over. In response, a representative man of the group told her as long as a Chess was still alive, the war would not end.

(Source: Wikipedia)