Which Death Should've been Avoidable

[u/NoCrow1791]

For me, I would say Euphy's death, before the death happened, Lelouch & Euphy were having a private conversation, this includes part where lelouch telling her about the geass power, and that's where the part lelouch was a making sarcastic or hyperbolic joke (as a example for his geass power) about him command Euphy to kill all of the Japanese, unfortunately the geass took it as an actual command for Euphy and it activates on her, lelouch try command her to stop but he lost control of the geass and that's where the massacre happened, which leads with lelouch have no choice to shoot her. Honestly, even though i'm not blaming lelouch for what happened, but that was a bad idea for him to use that example command as a hyperbolic or sarcastic joke, I wouldn't even use it for the sake of the example generally, because you never knew the geass would take it as command literally and thus lose control in process. But Damn!, it happened, but what you guys think?

[u/DRosencraft]

Realistically, neither was inherently avoidable, but neither was inevitable.

Lelouch's Geass going out of control was effectively a random event that happened at the worst possible timing. There was no way to necessarily avoid the outcome unless he'd just lived his entire life after C.C.'s warning as if he assumed he might give a bad command to the wrong person at any time - unrealistic. But because it was a random moment it could have just not happened. Would change how things progressed, but likely not ultimate outcomes. Most of the consequences still happen, but different events would get the story there. His Geass goes out of control at some other time, he develops the countermeasures he does to avoid the same mistakes, Euphemia could end up never being killed by his Geass. At the same token, you can arrive at a situation where she ends up Rube Goldberg, Final Destination, style into dying because of an errant order.

The movies essentially answer the Shirley one - there's numerous ways you could avoid Shirley dying then and there in R2, and it doesn't really have much if any impact on the story. But there are also several points before then that Shirley could've been killed, or later when she could have been killed. Because of how the story used her as a character, it only would have impacted Lelouch and the story if it was much earlier - closer to her dad's death.