Plot
Please Teacher! is a story mainly revolving around a tight-knit group of friends in high school and how they cope with several life-changing events that are never too far off from intimate relationships. The main character is a boy named Kei Kusanagi who has a very rare disease which causes a comatose state referred to as a "standstill" whenever he is under severe emotional distress.
Before the beginning of the story, Kei, at 15 years of age, had fallen into a "standstill" lasting three years after witnessing the suicide of his elder sister. After recovering, he quietly moved away from home in order to avoid social difficulty due to his long absence, and began living with his uncle, a medical doctor, and aunt. Due to the strange nature of how he came to live there, Kei wanted to keep the situation a secret from his new friends for fear of being ostracized as being too old to associate with them. After Kei had established himself in his new surroundings and had entered into a close group of mutually supportive friends, a Galactic Federation starship had entered Earth's atmosphere stealthily, approached Honshū Island and landed surreptitiously in Lake Kizaki.
The story begins with Kei suffering a minor 'standstill' while in the vicinity of the lake, witnessing several unexplainable phenomena happening there, and then watching as a beautiful half-human alien named Mizuho Kazami materialize beside the shore. Kazami was sent to observe planet Earth by a seemingly benevolent Galactic Federation in order to prevent humans from making developmental mistakes. Kei, upon observing the materialization, attempts to escape the pursuing Kazami. Kazami is under strict orders to prevent her true identity and mission from being discovered. During his attempt to escape, Kei falls into the lake. Kazami rescues Kei and, using information from his identification, is able to return him home in secret. The next day, Kazami has become Kei's new homeroom teacher and next-door neighbor.
During assisting her in moving in, Kei suffers another standstill, and while in a weakened state explains his predicament to the compassionate Mizuho, who ends up revealing her own origins and purpose on Earth. Several accidental activations of Mizuho's teleport technology (which were inadvertently caused by Kei) eventually place Kei and Mizuho in a couple of compromising situations in front of his uncle and aunt and his school's headmaster, but Kei protects Mizuho from charges for an inappropriate relationship between student and teacher by impulsively stating that they are married, resulting in an actual civil marriage that later blossoms into genuine affection for each other. The headmaster relents, partly because he, too, had married a former student younger than himself and can understand their situation personally. Both are allowed to stay so long as they do not reveal their status to the other students, and do not engage in any public displays of affection.
The remainder of the series concerns the budding intimate relationships between the close friends, one of whom (Koishi Herikawa) is romantically interested in Kei, and another (Ichigo Morino) who has suffered even greater loss of time from the same disease as he has; the problems of having to maintain the secrecy of the marriage; an interfering parent and sibling visiting from the Galaxy Federation; and Kei learning to overcome the ever-present threat of another lengthy 'standstill' stealing more of his life, particularly as he has fallen deeply in love with Mizuho and desperately wants to remain with her.
Eventually Kei falls into another major "standstill" and in order to bring him out of it, Mizuho has to use her technology which is against the law. As a result, her status on Earth is revoked, she is banned from the planet and all memory of her is erased from everyone's, including Kei's, minds. With the help of her mother and sister she sneaks back and is devastated to learn that Kei, who she is deeply in love with, has no memory of her. While helping her move back in, Kei reveals that his memory has returned and the two express their love for each other and get married again.
