Hazrat Mahdi (as) has a powerful urge to defend Islam

In the hadiths it is revealed that Hazrat Mahdi’s (as) protective instincts are very powerful. He will respond to every word spoken and neutralize every action taken against Islam.

Even a single word spoken against Islam will offend him. (Ibn Hajar al-Haythami, Al-Qawl al-Mukhtasar fi `Alamat al-Mahdi al-Muntadhar, p. 30)