Zenitsu was a crybaby and a scaredy cat before but now he becomes serious.. because his gramps died.. his gramps slit his own stomach alone no one beheaded him..because it's all zenitsu's seniors fault, because his senior turned into a demon..that demon name is Kaigaku.. that's why Zenitsu gets angry and wanted to beheaded him..(Their are sixth forms of thunder/lightning breathing the strongest one was seventh form but it will reveal if zenitsu behead Kaigaku).