Hidden Bullet: The Funeral Flower Withers is the last and main chapter in the 4th volume of Reborn! Hidden Bullet series. It tells the details of how Bluebell joined the Millefiore as the Rain Funeral Wreath.
Bluebell's flashback started with her drowning in a school's pool, which was pretty close to the hospital which Bluebell was staying in. Then, everything blacked out as a mysterious man saved Bluebell.
When she woke up, she was back into her room in the hospital. It was then revealed that Bluebell thinks 'water' is her only friend. She felt like that water was where she belongs to, as being in water makes her feel free.
That was why she tried to stood up to return to the pool. But she fell as her legs weren't able to support her weight. She almost dropped her friend (a cup of water) onto the floor but Byakuran caught it for her. Just as Byakuran spoke, Bluebell thought that the gentle voice was similar to that of her brother's. It was unknown if Byakuran looked similar to Bluebell's brother physically but it seemed that Bluebell think that Byakuran held great resemblance to her brother.
Then the time was skipped to the third day since Bluebell met Byakuran. It was revealed that Byakuran was hired by Bluebell's parents as a counseling psychologist and followed Bluebell everywhere she goes in place of her parents. And Bluebell was sneaking off to a pool again, she even crawled all the way there as Byakuran confiscated Bluebell's wheelchair to prevent her from escaping. Of course, Byakuran soon found her and carried her back. During the conversation on the way back, Bluebell's brother was mentioned which caused her to breakdown and thrash around in Byakuran's arms. Byakuran did no move to stop or drop her and just waited her to lose her conscious due to fatigue.
When Bluebell woke up, she was in the hospital again. And once again, she mistook Byakuran as her brother. Then, Bluebell remembered the accident which involved her older brother two months ago.
It was on the day when the nation-wide swimming competition which Bluebell joined was held. Her brother was, surprisingly, late for her competition that day. That's why Bluebell was so anxious that she kept looking around instead of doing warm-ups like the other contestants. Finally she spotted her brother across the street and ran to him without a second thought. But the traffic light was red at the moment, and a car came rushing at her. Her brother dashed forward to push her out of the way. However, Bluebell's legs were immobilized and her brother lost his life as the result. Then, it was revealed that Bluebell was so obsessed with swimming because her brother always praised her speed in swimming.