Koike-teacher's marriage proposal is an episode of the 2012 anime.
Synopsis[]
The episode starts with Kenichi bidding farewell to Aiko-sensei and Mr Koike. He then heads for the staircase, but stops dead in his tracks as he remembers that he forgot his gym clothes. As he goes back to class to fetch them, he sees Aiko-sensei asking Mr Koike if he would like to go to the museum with her on Sunday. He tells her that he'd want to, but he suddenly remembers that he has other commitments on the date they have fixed. Aiko-sensei doesn't mind, however; and decides to go with one of her girlfriends.
Back at home, Kenichi tells Hattori about Mr Koike's odd behaviour in school. Shinzo innocently suggests that Mr Koike fancies Aiko-sensei, which takes everyone by surprise.
That Sunday, Kenichi is grumbling because Mrs Mitsuba has given him, Hattori, Shinzo and Shishimaru work. Just then, he and Hattori see Mr Koike flirting with another woman. They are shocked even more when Aiko-sensei turns up unexpectedly. She sees Mr Koike handing the lady a box, and wonders if he is trying to propose to her.
The next day, on his way out, Mr Koike drops his diary. Aiko-sensei finds it and tries to stop him, but is unsuccessful. Later on in the park, Kenichi, Hattori, Shinzo and Shishimaru are playing football when they meet Aiko-sensei, who is searching for him so that she can give him his diary. Just then, they see him dart past, so Hattori and Aiko-sensei follow him. Just then, they see him talking to another lady, who gives him a box - and, just seconds later - to another one. The following morning, Aiko-sensei gives Mr Koike his diary, and tells him that he can take one of his girls to the museum. Mr Koike is downcast, and acts strange for the rest of the day.
At the park, Kenichi tells Hattori, Shinzo and Shishimaru about Mr Koike, and Hattori suggests they all go to talk to him. That evening, they see him at school, in loud, noisy tears. They consult him, and discover his reasons for his state of sadness. In another part of the school, Aiko-sensei decides to apologise to Mr Koike; however, she is baffled to see him getting a box from another lady - a box of butterflies. They find out that he was exchanging butterfly collections with other butterfly collectors.