Riku was good at math, but he hated speaking in front of the class.

On Friday, he had to explain one problem on the board. His hands felt cold before the lesson even started.

Mina sat beside him and noticed his notebook shaking.

"You know the answer," she whispered.

"Knowing it and saying it are different," Riku said.

Mina opened her pencil case. Inside were many small star stickers. She placed a gold one on the corner of his notebook.

"This is not magic," she said. "It is a promise."

"What promise?"

"If you try, I will clap first."

When the teacher called his name, Riku carried his notebook to the board. The star sticker caught the light.

His voice shook at first, but the numbers were clear. Step by step, he explained the problem.

When he finished, the room was quiet for one second.

Then Mina clapped. Other students followed.

Riku returned to his seat and looked at the star.

"It worked," he said.

"No," Mina said. "You worked."

Riku smiled and left the sticker on his notebook.

The next week, when Mina looked nervous before her English speech, Riku gave her a blue star.

"Same promise," he said.