If you read Gurren/Lancelot manga what is the gist of Rolo and Benio's interactions during the geass cult massacare and before the betrayal?
You ask for the gist, but I just translated everything! All scans taken from https://comic.webnewtype.com/contents/geass_g/, which used to offer all chapters for free (but they don't anymore?). There will be spoilers for what happens to Benio and Savitri at the end.
I haven't read the whole manga, just the parts with Rolo, but I think the first time he shows up is when he sees Zero talking to Benio in a friendly manner (asking if she has any siblings, since Kallen and her act like sisters) and his reaction is as expected:
He is later annoyed by her hesitation during the Geass cult massacre:
Rolo "It's a problem if you don't bring them down properly." Then he thinks (2nd panel, thoughts next to Vincent) "This person... If I remember correctly she was acting friendly around Zero"
Benio "... This is wrong. It's the same as Britannia that day..." referring to what Euphy did.
Rolo "? What are you talking about? There's nothing wrong. Zero ordered that we annihilate them."
"You and that Kinoshita from earlier. Saying things that make no sense..." This is enough for him to decide to kill Benio without Zero's permission. Well, what else did we expect.
Benio has been waiting for a chance to talk to Zero. Rolo calls her, claiming that Zero asked for her "to come here."
Rolo "He's sorry that he couldn't talk to you earlier but it seems he could find some time now" Benio "Really? Thank you so much! I have to go to Ikaruga's office, right?" Rolo "No, he wants you to come to Ikaruga's dock. Alone, of course" Benio "Understood!" Savitri "... Who was that?" Benio "That person called Rolo. He says Zero wants to see me, so I'll be back soon!" Savitri "Rolo? .... I see. That's strange..." In the next page Savitri remembers that Rolo is that creepy yandere stalker:
So Benio meets Rolo:
Benio ".... Is it really here...?" Rolo "It's here." Benio, that's clearly the villain! Run!
Benio "Rolo-san! I'm glad. You will let me meet Zero, right?" Rolo "Of course. He is a bit late, but will come here soon" By the way, she speaks in formal Japanese, while he doesn't. I guess he's the senpai (which means he joined the Black Knights earlier than Turn 14? Well, Vincent more or less already became part of the BK in Turn 4...) Rolo "Hey, Benio. You wanted to meet Zero to talk to him, isn't it? What did you want to talk about?" Benio "Um... That's..." Rolo "Something you can't tell me?" Benio "..." I'm smiling nicely, there's nothing to fear!
In fact, she does answer Rolo's question. She wants to talk to Zero to know the reasons for massacring the Geass cult. She thinks only Zero might be able to give her an explanation that she can find acceptable.
Rolo "... ..." Benio "Rolo-san...?" Rolo "... All the people that Brother cares about end up betraying him. Such trivial distrust will spread to everyone and they might betray Brother." Benio "Em...?" Rolo "Haha."
Rolo "I knew he didn't need them. Brother needs no one else besides me." Well done Rolo, you found a excuse to justify killing yet another innocent girl!!
Savitri "Wait!!" Benio "Savitri!?" Rolo "See? You can't be trusted. I told you to come alone, didn't I?" Savitri "I came here on my own!"
Savitri "You are the one who should explain what your intention-"
Benio "Savitri!" Savitri "Be... ni... Run..." Benio "What's happening...?"
Benio "I didn't see him approach Savitri. I don't understand what happened. But I know this person did it..."
Rolo "... I've been overusing my power lately. I wanted to finish you both at the same time, but I failed... It seems the wound was a bit too superficial... Well, I don't really need Geass, do I..."
Rolo "No matter what, the result will be the same"
Rolo "Aah, I knew this would be bothersome." Anime villain lines™
Rolo "I will finish you with Geass." Benio "That thing from before. It's coming!" ??? "What are you doing!"
Zero "Stop it, Rolo!" Rolo "Brothe..."
Zero came here after hearing that Rakshata was trying to contact Savitri and couldn't reach her. He asks Rolo for an explanation.
Rolo "It's for Brother's and... the Black Knights' sake." Sure it is, Rolo Rolo "During the Geass Cult annihilation operation, Benio didn't shoot! Someone with high combat skills and who knows about the Geass Cult... What will happen if she is a traitor! We have to kill her, Brother! Savitri is equally guilty as her collaborator!" Let's kill everyone!!
Zero "... Benio, why didn't you shoot?" Benio "... Because I didn't want to be like Britannia. I didn't want to trample on weaker people."
Benio "Because we are allies of justice." Rolo "... It's clear now. Benio has doubts about Brother's policy. She's saying that she can't follow your rules. She's a useless pawn now. We should kill her as soon as possible. That's the best for Brother."
Zero "Allies of justice... I see." Rolo "Brother!" Zero "Rolo, don't worry. I'll make them forget"
Zero "Everything..." And so that's where Rolo's part ends, and Benio and Savitri's current stories end as well. They forget everything and are shown to lead happy lives outside of the Black Knights without these memories. Maybe this was way too long a reply to the ask, but I tend to like translating as much as possible haha.
