Kei Kusanagi, an Ordinary High-School Student, has just seen an alien.Problem is, she's just announced herself as his new Homeroom teacher, Mizuho Kazami. And she just moved in next door.And the last time he saw her, she tried to wipe his memory of her existence.One would think a situation like this would not end well, but a few hijinks later they end up married after Kei reveals that he's older than he looks to prevent a potentially compromising situation from being taken the wrong way).Unfortunately, now they have to keep his age, her origins, and their marriage a secret from Kei's friends, which is going to be difficult, as one of them is starting to get aggressive in trying to catch Kei's attention.Please Twins! is a Spin-Off involving different characters at the same school. Ano Natsu De Matteru, the third anime series of the franchise, is either a sequel or a reboot with new characters.
Beach Episode: Episode 5, which is also Kei and Mizuho's honeymoon. No one they know is supposed to be there, but of course, Kei's friends and one of the other teachers all just also happened to be there as well...
For Ichigo, it was coming out of her long coma to discover her little sister was now a married adult.
For Kei, it was watching his older sister commit suicide by jumping off the school roof.
Double Standard: Rape, Female on Male: Okay it doesn't go as far as actual sex and she was trying to add spice to Kei's life with Mizuho but in the OVA Hatsuho forces Kei to go with her to a love hotel and ties him to a bed while looming over him with something that looks suspiciously like a dildo while he makes his displeasure clear. Were the genders reversed this would be very creepy.
Dude Hes Like In A Coma: Mizuho kisses Kei for the first time while he's in a standstill (it was Kei's first kiss too!)
Ecchi: This goes to extremes and very veryVERY close to hentai in the epilogue episode. So close that anyone that forgets that this isn't an H-anime would probably be disappointed.
Ill Boy: Played with: Kei's Angst Coma disorder is not debilitating or life-threatening but they have to keep it a secret because it could unravel all of their other secrets as well. It does worry Mizuho every time he keels over, though.
Innocent Fanservice Girl: Perhaps not fully applied given as how each remotely attractive female on the show (that is to say, all of them) has at least some idea of the influence her looks have, but there are plenty of times where they don't realize the effect they have.
Not What It Looks Like: Used at least once (if not more) in practically every single episode. Not to mention that it basically fuels the plot 90% of the time. (The rest of the time it is what it looks like and they have to pretend it isn't.)
Primal Scene: Done for Maho for humor, possibly due to alien biology causing her to be Older Than They Look. She makes films of Kei and Mizuho's night life and blackmails him using them. Apparently Hatsuho doesn't know this as she does the exact same thing when she sets them up in a Love Hotel and Maho says she wants to see the video chips, which the former says are for "adults only."
An alternative possibility is that Maho didn't film anything, but Hatsuho told her to blackmail Kei by pretending she had. Maho is shown later asking Hatsuho why her scheme was so elaborate that she actually had a script for it, to which her mother's reply is also rather cryptic. Maho may not have had any idea what was actually supposed to be on the video chips she showed Kei.
Reset Button: The Federation forces everyone to forget Mizuho and puts Earth under a quarantine. Mizuho sneaks back and breaks through Kei's Wistful Amnesia. Then they get to redo their relationship from the beginning, with the implication that it all went much smoother this time.
Secret Relationship: Kei and Mizuho can't be open about their marriage largely because it'll be seen the wrong way by both the faculty (aside from the principal who already knows but tells the two not to openly show feelings for each other in public), and Kei's friends. Hilarity Ensues a lot due to this trope.
Shipper on Deck: Ichigo does this for Kei and Koishi. And later Kaede and Hyosuke.
Teacher/Student Romance: Obviously the title characters and the plot of the series. Furthermore, they get away with this because not only is Kei really 18 (and therefore legally old enough to marry the teacher), the school principal married a student as soon as she graduated and sympathizes with them. Kei gets creeped out.
Twenty Minutes into the Future: Mizuho's human father was a member of the first attempted manned Mars mission, which is stated to have occurred in 2009. Assuming she ages the same as normal humans, the earliest this series could take place would be the early 2030s.
Which is weird due to the apparent lack of cellphones.
Wistful Amnesia: Kei just can't shake the feeling that something (or someone) is missing from his life.