I saw it coming even before the spoilers, but seeing it for real is a whole different beast ;_;
I'm so proud of Kazuya, he doesn't even say a word, he barges in, sets it up, and leaves so she can have a moment with her grandma. Doesn't try and butt in and watch it with them, doesn't make any grand statements about saving the day, this seems like a genuine selfless act. He's not even flustered! He probably hasn't even had the chance to watch it himself, but he's finally thinking about nothing other than making the Grandma's and her's final moments as beautiful as possible. As much as she went on about how she has no regrets, it's also well established that it's just a persona she projects, as soon as she's behind closed doors, her Id is revealed. She would've been haunted by the thought of not showing her grandma the movie no matter what she tries to say outwardly. This is Kazuya's best moment easily and it's because it might've been the first time he did something without ulterior motive. Well done Mangaka! You've believably took a man from saying he's looking out for others to actually looking out for others silently.