Shiizou Atsukuru (熱繰 椎造 Atsukuru Shiizō) is 22 years old and worked for a while as Futaba Kindergarten staff member as a teacher in training in the Sunflower class. He first appeared in episode 541b. He can literally be on fire at his own discretion, which is his key personality trait in the show. His name is a reflection of this as it is wordplay on the expression "atsukurushii zo!" (暑苦しいぞ！), which means "It's sweltering!". At first, many of the students were taken aback and annoyed at his passionate way of teaching things but they grew to love him in the end.
In the manga he is introduced as a replacement of Midori since she was pregnant, in the anime this never happened so he is just introduced as a new coach with Midori still working in the Kindergarten.