Bayer is the Boötes saint of the Century XXI. He is loyal to Athena, but thinks she is Aria, and Mars is an Athena new ally, so, obey his orders.
His importance in the story is insignificant.
Bayer was the one of the 3 protector of the Thunder Ruin's guardians... He attacks all the bronze saints, but Ryuho decides to fight him to distract him while Kouga, Yuna, Souma, Haruto and Shaina move on. Bayer is defeated, but survives.
After the war ends, Bayer goes to fight against Pallas, as a hero that know who is the true Athena. As a good guy, he goes to fight in Pallasbelda, against the soldiers of Dione.