The heart option in season 5 episode 3 has Monarch accompany Renzei and Andi to an Optimus training facility, where Renzei grieves, talking about his past with Optimus before cathartically tearing apart the place with the other two.
Renzei:I was eighteen when they first brought me here. I was just a kid. I gave them my whole life, and they repaid me by killing my family, the only people I loved.
In the third episode of Renzei's second season, he and Monarch reveal their betrayal to the Syndicate and leave the team for Optimus, abandoning the others to Ajax and his army of mooks. The reactions from Duke, Andi, Lorelei, and Bat are a gut-wrenching combination of shocked, confused disbelief and hurt; even after Monarch directly calls Duke out for having Renzei do the Syndicate's dirty work, it's clear that none of them want to believe what's happening.
Maybe the truth is that if you push someone into the right place, anyone can be a villain. Monarch: (Including me.)
In a heart scene in his second season, Renzei explains the significance of his tattoos: they're a tally system, commemorating each person he has killed, so that he can never forget or look away from what he's done. In the process of explaining this, he reveals that he made his first kill before he was old enough to drink, and that he expects the tattoo to eventually extend all the way across his back.
Renzei: I want to remember. I need to. ... I should be aware of it all, and it should hurt.
Season two keeps the tears coming. As they set out on their mission to murder Duke for Optimus, Renzei struggles to even identify how he feels about what they're doing. He finally, painfully admits that he doesn't want to complete the mission... but when the moment passes, he pushes his feelings aside again and lapses back into expressionless calm. Monarch asks him how he does it:
Renzei: The cool answer is that I'm a stone-cold professional. Monarch: I want the real answer. Renzei: I think about hugging my mom again someday. It steels me.