I'm not sure about a specific title right now, but you can often find some on fanfic platforms. Look for ones with high ratings and positive reviews. Usually, those are the ones that do a great job of portraying Kotoura and Manabe's relationship in an interesting and engaging way.
One great Kotoura x Manabe fanfic is 'The Unspoken Bond'. It beautifully explores their relationship, delving into the deeper emotions and unspoken feelings between them. The story has a great pacing, gradually building up their connection.
There is a fanfic called 'Our Shared World'. It starts with a simple encounter between Kotoura and Manabe and then blossoms into a story about how they support each other through various challenges. It really captures the essence of their characters and how they could interact in different situations.