After that, several calls came again, but Theo ignored them and continued searching for missions. If his joker identity got targeted, he simply changed back to Theo.
At the very least, there wouldn't be a problem within the first month since he would have gone somewhere.
And the moment they chased his Joker identity, he switched to Theo and reached level 350 with that identity. The Lange Family should be searching for Theo's real identity and might have found him, so there was no need to hide it anymore.
By that time, he should have finished his training and met his brother. Not long after that, there would be someone from the Griffith Family meeting him. He only needed to leave everything behind and go to another country.
And with them chasing Joker or Theo, he could publicly shame them and have another country release a statement that he fled from Thersland because he was threatened by them.
