Riser is Karlamine's master. Nothing else is known about their relationship other than that some time before the start of the series, Karlamine entered Riser's female only peerage as his Knight. Karlamine is loyal to Riser, faithfully following his orders even when it opposes her honor as a knight.
Karlamine views Yuuto as a worthy opponent both following the same honor of a knight. She also willingly admit that she lost to Yuuto after Yuuto uses the boosted power given by Issei to unleash his Sword Birth.
Karlamine has shown some respect to Issei's skills for being able to defeat Isabela but is disgusted by his shameless move at the same time.