Found a way

[Next day]

Demon came with breakfast and saw the siblings still sleeping.

"Aster, Hisha, breakfast has arrived."

They woke up and saw Demon.

Hisha walked over to the fountain to wash her face, she dropped her head in and came back up fully awake now.

After breakfast Sebastian came with all the green books.

She looked through it and found what she was looking for.

She took one shard and used her magic.

The crystal melted and whatever was inside also burned.

Hisha called out for her father at the front door because she was scared to get inside.

Demon heard her, he and Aster came outside.

"What is it sister?"

'Look, fire kills.'

'But if stone is big, Hisha can't do it.'

Demon picked her up. "Don't worry you and your brother are the strongest in wielding fire magic. You both hold a lot of mana so I know you can do it."

She smiled and nodded.