Reasons

Shoutout to Daoist906861. May you tank diff an Orisa as Rein in your next game. 

We sat there in silence. I knew my place for it was on Mamoru to decide and not mine to speak for him, so I refused to answer or even show how this affected me. But from sitting so close to Mamoru, I could feel from his bioelectricity, that he was in turmoil. Suddenly, Mamoru stands up and begins walking towards the gate. In surprise, I follow him, but not before taking a final look back at the elders. Seeing the pleased looks on their faces tells me that we're doing exactly what they want.

They let us out, and we begin to silently walk the streets, walking further away from Shimada castle. Knowing the pain that he's going through, I refrain from saying anything. But, as I notice that we enter an area where the streets are a bit rougher and clear thugs blatantly wander the streets, I know I have to address the issue. 

"You can't be seriously about to do it?" I question.

"I have little choice." He responds solemnly. 

"Ok, I mean, the witch, yes. But you don't have to kill Gen... I mean his son. Like they didn't even offer you anything for doing it, like getting reinstated back into the clan." 

"Once someone is banished, the decision can't be unmade. Not by the elders and certain not by my brother. It would set a bad precedent, where anyone banished could just perform acts to redeem themselves." He explains. 

"Listen, I can understand the situation you're in, and I'm not trying to be a naysayer or anything like that. I'm just trying to see if you've thought this through fully, like all the way into the bone. You and I both know that we'll be doing their dirty work for them. That they'll take the credit should this somehow work out. That their hands remain clean and blameless should we mess up. The real question is are you ok with living the rest of your life knowing that you took out your brothers' son?"

He pauses, turning slowly to me. Although his face doesn't show it, I can see the hurt, and pain conflicting inside of him at my words, but I didn't care, he needed to process this. All his life he just did things without thinking about it and suffering the consequences afterward. As his apprentice, his partner, his friend, I needed him to think this one through. 

We step aside into an alley away from the streets as he leans against the wall. Pulling out a cigarette, he offers me one. Usually I wouldn't have, but given the situation, I take one. After we both take a puff, he waits for me to stop my fits of coughing before responding. 

"Of course, I know that we'll be doing their dirty work for them. Of course, I know that we'll be the fall guy if things go wrong. And things most certainly will go wrong. Why will I do it? Because if I don't, who will? 

Would I be capable of doing such a heinous act of killing my brothers' son? Easily. It would bother me more if I didn't do anything. How am I capable? I long ago, knew that I was that guy, who would have to get his hands dirty so that my brother wouldn't have to. Would he be furious when he comes to and finds out what I've done? Maybe. Probably even go as far as execute me. But, that's fine, because when all is said and done, he'll be able to continue with his life with Hanzo, hopefully peacefully. 

Now, are you going to help me or not?" 

"Yeah. Lets do it." I respond stomping out my cigarette. 

He keeps his in his mouth, as we both turn the corner. In front of us, was a group of Hashimoto thugs, obviously grunts. No doubt we were going to capture one and find out their base of operations. 

The five notice us and immediately turn serious, possibly they recognized Mamoru, or they could read our expressions. Looking over each of them, I knew they were light work, barely a challenge. 

"What me to handle this?" I ask.

"No, I have some steam to let off." Mamoru says and I step back. The grunts look at each other before rushing him together. Unfazed, Mamoru stands there, until the first grunt reaches him. The grunt flies at him, swinging a pipe in front of him towards Mamoru. He easily steps back letting the attack miss him as he counters so fast that I have to focus in order to catch his movements. His hand swipes across the guy's throat as he steps past him, leaving the grunt clutching at his throat. 

Seeing what happened to their companion, three grunts reach him at the same time, looking to avenge their fallen friend. They each strike out at Mamoru, each deseparate to land a hit against him. Mamoru dances in-between their strikes, taking his time to find an opening. After a couple of seconds, his hand darts out, stopping the oncoming blade of one of the grunts, as his other hand shoots out, hitting the neck of that grunt. 

The other two begin to panic, their attacks growing frantic as they try to at least hit him once. One of the grunts misses, and Mamroru steps in close, his hand hitting the grunt three times in the stomach, leaving him grasping his bleeding stomach. The last guy brings his baseball bat down towards him. Easily sidestepping it, Mamoru steps past the guy, bringing his hand past the guys neck. 

The final grunt who witnessed everything, drops his weapon, as he begins pleading for his life. Mamoru simply grabs his hair, pulling him into a nearby abandoned building. I stand guard outside, listening as the building does an ok job of isolating the guy's screams. After half an hour, the guy silences and Mamoru walks out, lighting a new cigarette. 

"Wanna ask the next one some questions this time?" I ask sarcastically.

"I said I had steam to let off. Plus, I doubt these low-level grunts would know anything. There's only one question I would have to ask them." He elaborates. 

He intentionally doesn't reveal the question, leaving me to think what it will be. On an operation like this, I also wouldn't make the knowledge of whats going on commonplace. But inevitably, someone would be bound to have an idea of who would know what's going on. So, it's just a matter of us finding someone who knows someone who knows.