‘As little as two minutes,’ Mizuki said. ‘In four to six minutes of drowning, a person can sustain permanent brain damage.’ Her fingers grazed the window frame. ‘By contrast, a human can hold their breath for more than five minutes. Interesting, isn’t it? The key is preparation. Breathe slowly for several minutes and, before you dive in, take a deep breath.’

‘Mizuki …’

‘Don’t you think it’s strange? It didn’t occur to us to try to revive her,’ she said. ‘I kept thinking about that afternoon, even months after. Umi could have fainted. I tried singing Happy Birthday three times and timed it. Even adding in the time between the songs, it should only take about two to three minutes. She wasn’t dead when we pulled her out of the pool. My sister might still be around if we had called the paramedics instead of trying to cover up our foolish act.’

‘You were in a panic. She wasn’t breathing, was she? Anyone would’ve thought she was dead, and then the survival instinct kicked in.’

Mizuki shook her head. ‘No matter what, we killed her. That’s a fact. Let’s not gloss over it.’ She returned to her seat. ‘We could’ve saved my sister if we hadn’t tried desperately to save ourselves first. We decided to sacrifice Umi. We chose to live in denial, but her death continued to echo in our lives.’

Shoji felt a lump in his throat. None of them had wanted the accident to happen, but the reality was that a life had been lost.

But something about the story was strange. ‘You said your sister was bleeding, didn’t you? That shouldn’t happen if she had drowned and fainted.’

‘About that …’ Mizuki paused. ‘It’s a woman’s thing, you know.’

He hesitated. ‘Was she menstruating?’

‘Yes, she got her first period ahead of me. That was probably what had made her upset. Umi hated growing up. She had always been slightly bigger than me. She was taller and her breasts were more developed. I used to be jealous of her.’ Mizuki turned to Shoji. ‘It’s silly. We’re always dissatisfied with ourselves.’

‘Uh-huh. What happened to the other two?’

‘We never spoke to each other after the accident,’ she said, ‘but I still saw them around, since we were schoolmates. My sister’s boyfriend was the star of the basketball club. After Umi’s death, he quit the team and became a delinquent. Less than a year later he died in a freak accident. He got drunk and fell from a high-rise building. But who knows?’

‘You might be overthinking it.’

‘Possibly,’ Mizuki said. ‘The other boy was an average guy. He disappeared. He’d never been remarkable, other than the fact that he was Umi’s boyfriend’s best friend.’