Umm, I don't really know what to say. I'm really sorry guys. *hides under bed in shame* Slight movie spoilers, I guess.
Mayuri is different now. The old Mayuri—cheerful, talkative, laughing—has been replaced by a quiet, sad stranger. She'd cried the whole time during her grandmother's funeral, but now the crying has stopped she just seems sad and empty. Okabe wishes he could fix it, wishes he could make his friend smile again, but unless he can magically bring her grandmother back to life, he doesn't see any way to make this better. Mayuri's depression and hopelessness almost seem to be contagious, and he finds himself consumed with fear for his friend.
The next day, he runs into a strange girl on his way to meet Mayuri at the graveyard. The entire encounter is bizarre, to say the least, but it does give him an idea on how to get through to his friend. So he takes off running, determined to remedy the situation while he still has time. It's simple, of course. All he really has to do is remind Mayuri of how much he cares about her, and that she'll never be alone as long as he's around.
The next day, the rain has finally stopped, and although Mayuri still goes by the graveyard after school, she only makes a short visit. And afterwards, when she begs Okabe to tell her about the stars, she's finally smiling again. It's a small smile, but it makes the world seem brighter already.
Okabe is different now. He tries not to show it, but he constantly seems tired and sad. Mayuri tries everything to cheer him up and distract him from whatever is bothering him so much, but nothing seems to be working, and Mayuri can't help but feel that it must be her fault.
She's always been able to cheer up Okarin when he's sad, but now she feels like he's in a different world, and no matter how hard she tries, she can't get through to him at all. She wonders if it's because he has other friends now, and wants to spend time with them instead of her. That thought makes her sad, and she tries to push it away and focus on the positive. There doesn't seem to be that many positives though. Or maybe it has something to do with the horrible dreams she keeps having.
She tries talking about it with Gran, but she's still at a loss on how to fix her best friend, especially now that he's practically a stranger. He goes with her to Comima for the first time, but she can't even bring herself to be happy about it, because he still looks so sad and lost, and he's so distracted the entire time. She just wishes she could fix it.
Even after the dreams finally stop, and Mayuri knows that the bad things aren't going to happen anymore, he's still too quiet. When he drops the mad scientist act, Mayuri knows that this is her fault, and that he must have had to give up something precious to him for her to be safe. It makes feel her horribly guilty.
The day after the strange incident with what Okabe had called a time machine, she comes to visit him in the hospital as soon as school lets out. She's been worried sick, but fortunately he seems to be alright, if a little tired and pale. She immediately scolds him for being so reckless, but she's caught off guard when, halfway through her tirade, she notices that he's finally smiling again. It's just a small smile, but he seems to radiate contentment. She pauses, suddenly at a loss for words, and grabs his hand. For the first time in a while, she knows things are going to be fine.