"Pneumococcus" (肺炎球菌 Haien kyūkin?) is the 1st chapter of the Cells at Work! Manga. The anime adaptation for this chapter is also titled "Pneumococcus".


Inside a human's body, roughly 37.2 trillion cells work hard everyday endlessly to keep their host healthy. AE3803, a new, ditzy red blood cell was attacked by a group of pneumococcus bacteria during the midst of her job. U-1146, a neutrophil appeared in the nick of time and ruthlessly terminated the foreign entities, saving her. However, Pneumonia Coccus, the only surviving bacteria hid and escaped. Later on as AE3803 got lost and wandered around the body to search for her destination which is the lungs, she bumped into the escaped bacteria. Again, U-1146 managed to saved her but the pneumococcus escaped again. The two talked and reassured the situation, U-1146 offered help on bringing her to the lungs.

After a while they reached to the lungs, AE3803 left and went deeper into the lungs while U-1146 continued to search for the escaped bacteria. AE3803 then successfully arrived to her destination. Unexpectedly the pneumococcus jumped out of the boxed goods she was delivering, he hid inside the box when U-1146 appeared in before and received a free ride to the lungs. As the bacteria was about to cause trouble, U-1146 came in through transmigration and save AE3803 once again. After putting up a tough fight with U-1146, the pneumococcus was later sent out the body through a sneeze.

AE3803 thanked U-1146 and then parted ways.

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