Equuleus, Subaru

小馬座（エクレウス）の昴

Subaru is a member of the technologically enhanced special backup unit for Athena's Saints, created decades ago by Steel Saint Mitsumasa Kido.
One day, after learning about Pegasus Koga and his deeds—specifically climbing the Twelve Temples and defeating both Mars and Abzu—he appeared at a Steel Saint training facility. He trained harder than anyone, never speaking to anyone, until one day he met Erna, another Steel Saint. He spoke to his new friend, declaring his intention to become like Koga, and to defeat him.