If anyone watches the Soul eater franchise, they would know that the most annoying character is Excalibur, by a large margin.
Hiro is the only one who could put up with it (for a while), but despite being the single weakest student at death academy, he was able to instantly defeat 3 of the strongest students, including shinigami's own son, with infinitesimal effort, due to the power of excalibur.
Scenario: Excalibur did not catch a cold, so Hiro did not get rid of him. Hiro over the course of many months learns a lot about how to use Excalibur to its potential, including unlocking all its techniques.
Vs shinigami at peak power