It Seems We're Well Matched - S1.E10

The four begin to battle and Kazuki eventually inflicts a fatal wound on Shusui. Ouka uses her buso renkin and heals Shusui while at the same time receiving Shusui's wound on her own body. Due to this, Kazuki realizes they are both humans and not Homunculi and questions whether they are the enemy or not. Shusui reveals that they worked under the LXE so that one day the two can become Homunculi and live together for eternity.