Magia Record Story Always Waving my Hand at You
The following is a summary posted on 4chan's /pmmm/ general.
Sakuya killed her best friend during the Crimson Resolve event and got PTSD, not being able to sleep well at night. Yet she was sent to Iroha's school to collect intel on Kamihama.
She dropped her guard initially and joined the track team, getting close to her schoolmates and team members. But then she remembered her role, and the fear of killing friends again if these girls are either magical girls or related to them scared her, so she pushed them away, first by trying to quit the team, then by bad-mouthing herself in an anonymous class chat room and building up the image that she is being bullied to protect herself.
But her cover broke apart when she was rescued by Ryoko of the Tokime Tribe. Ryoko admired Sakuya's footwork as she fights a witch and helps her finish it off when she lost her breath. She gave the grief seed to her but fell due to hunger. She decides that Sakuya is someone worthy to be her friend judging from how she is willing to share food despite being on different sides, and on how well toned and shaped her legs are: only obtainable by someone with diligence and hard work. Sakuya has mixed feelings about Ryoko's straight forward approach, but she does suffer less and less from the nightmares. This frightened her as she thought it meant she was forgetting her friend and also at the possibility of killing another friend. Thus, she tried pushing Ryoko away.
However, unlike her brash methods and direct personality, Ryoko is very resourceful as she deducted that Sakuya is behind the bullying of herself, and she also managed to get info from Ranka at the Traveling Adjustor's place (Ryoko's target was the Adjustor, but she knows nothing, so Ranka who is also worried about Sakuya, told Ryoko about their city).
Ryoko challenged Sakuya to a fight at lakeside, acting as her punching bag as she claims she will not die so easily nor will she choose to kill since she is a Buddhist.
The fact that they are on different sides is exactly why they should become friends: they might lose this opportunity when the conflict actually begins, so it is like borrowing time from the future.
Sakuya failed to kill Ryoko despite her being tired and hungry from getting info about Sakuya for the whole day and relents. She also remembers her best friend telling her to look forward and live a good life, forgetting her as they have tried their best.
Sakuya took a compromise: she is friends with Ryoko at the restaurant she is treating her today only, and they really hit it off like childhood friends, talking about their daily life, dreams and plans for the future.
Eventually they depart and break up, wishing that they can resume the friendship after the mess. Sakuya thanks Ryoko for healing her PTSD, and Ryoko tells Sakuya she can come after her when they're on the battlefield since she will not die, and she need not worry about killing again.