Umi kept on trying to raise her head, but they pushed her down into the water. They knew she was a good swimmer. She could hold her breath for a long time. They had counted a couple of times, and she could stay underwater for almost four minutes. All of them remembered that, so they laughed and dunked her head.

One of the boys — Mizuki couldn’t remember which — started singing a Happy Birthday song. The rest of them joined in. Umi continued to struggle in the pool as they merrily sang the song.

Today is a happy day,

Today is a pleasant day.

Happy birthday to you,

Let’s sing a song.

Today is a happy day,

Today is a pleasant day.

Happy birthday to you,

Let’s sing a song.

‘One more time!’ someone shouted. ‘Let’s make today her birthday.’ They laughed, and then they sang again, from start to finish. On that balmy afternoon, the three high school students in their navy school uniforms sang the Happy Birthday song three times at the top of their lungs.

•

Mizuki laced her fingers together. She stared at them for a long time, biting her lower lip. The silence filled Professor Goda’s stylish office. Shoji hesitated. Should he tell her not to force herself if she didn’t want to talk about the incident? But she’d probably waited for a long time to have someone listen to her story, to share the burden she’d been keeping deep inside her all this time.

‘What happened after that?’ Shoji eventually asked.

Mizuki lifted her face. Her eyes were watery. ‘That day, my sister wasn’t feeling well. We caught her by surprise. She didn’t have time to take a deep breath before we pushed her in. Not knowing she was struggling for her life, we continued to hold her down until …’

No, this was too hard for her … Shoji looked into Mizuki’s eyes. ‘Are you all right?’

She nodded and mouthed, ‘I’m fine.’

‘It was an accident,’ he said. ‘Nobody wanted it to happen.’

‘The three of us killed her, and it was me who started it. The prank was my idea. I was the one who wanted to push her into the swimming pool. We only stopped when she was no longer moving.’

Shoji thought Mizuki was going to break down and cry, but she didn’t. She managed to keep her composure, but he could see from her stiff posture that she was hurting inside.

•

Realising what had happened, the teenagers stared at each other, frozen. No one said a word until one of the boys pulled Umi from the water. She was motionless. He laid Umi on the ground and brought his finger near her nose. A moment later, he turned to Mizuki. His face was pale.

‘She’s dead,’ he said in a small voice.