Because the magic used by Captain Eira was Forbidden Magic, which means she already knew the impact if she used that dangerous magic.
'I hope 5 minutes will be enough to defeat that mysterious man.' With confidence Captain Eira hoped that the short time was enough to defeat the mysterious man, or sooner so that she still had time to catch up with Colonel Lily and Princess Aurellia before she got side effects.
"Even though you look very excited but I can't play with you any longer." The mysterious man's voice sounded very confident and made Captain Eira very annoyed because she had been underestimated even though she was in her strongest state.