Theo thought for a moment and asked inwardly, 'Should I use my last trump card? But if I use it, I have to leave everyone…'
Theo couldn't help but remember Agata and all the people who were close to him. Agata would surely cry if he used that trump card. Even Leonardo, his grandfather, as well as Valerie and Ray, his parents, would be devastated. He couldn't keep his promise to his parents as well.
As for his group, it would be the biggest disaster. Rea might be able to replace him, but the fact that Theo was gone would be a tremendous hit to them.
Although he could still retain some power by asking the Heavenly Sovereign or Hel, it didn't change the fact that the group would basically be unable to function anymore.
That was why Theo never wanted to use the last trump card, if they could still somehow fight the slime.