Complex sentence: Keiko was the first one in go solo releasing her first single KCO in December 2003, and months later in 2004 Marc started her solo project under the pseudonym of 245, project that has plans for international projection beyond Japan.
Split into simpler sentences: Keiko was the first one to go solo, releasing her first single KCO in December 2003. Months later in 2004, Marc started her solo project under the pseudonym of 245, a project that has plans for international projection beyond Japan.