Zenitsu Agatsuma is an extremely powerful Demon Slayer known especially for his incredible speed and mastery of the Thunder Breathing technique. He is uniquely strong when unconscious or very focused, able to perform his signature "Thunderclap and Flash" attacks at lightning-fast speeds that can decapitate demons in a single strike. Despite initially being seen as weak and cowardly, Zenitsu repeatedly proves his strength by defeating powerful enemies including upper-rank demons such as Daki and Kaigaku. By the end of the story, he unlocks advanced techniques like "Godspeed" and a seventh form of Thunder Breathing, significantly boosting his leg strength, speed, stamina, and overall combat effectiveness. His power level rivals that of the Hashira, the elite Demon Slayers, and he can hold his own even against the Demon King Muzan in weakened states. His exceptional audio perception heightens his situational awareness, allowing him to anticipate dangers even while unconscious. Zenitsu is considered one of the fastest and most deadly swordsmen despite mastering only the first form of Thunder Breathing and creating variations of it to outmatch opponents.

In summary, Zenitsu is one of the strongest characters in the "Demon Slayer" series, known especially for speed, precision, and the devastating impact of his attacks, making him a formidable opponent despite his initially timid nature.