Starry Sky ～in Spring～ (released March 27, 2009): Capricorn, Pisces and Cancer
Starry Sky ～in Summer～ (released June 26, 2009): Taurus, Scorpio and Sagittarius
Starry Sky ～in Autumn～ (released September 25, 2009): Gemini, Leo and Libra
Starry Sky ～in Winter～ (released December 25, 2009): Aquarius, Aries and Virgo
Every game has a PSP port with additional content, as well as a 3DS port. They also have their own fandiscs, subtitled After with the name of each season (also ported to the PSP), and an anime, released between December 2010 and June 2011, by Studio DEEN.Each character has his own Drama CD, which were released throughout the year 2009. note Actually, the games were released as a way to provide context to the Drama CDs, but they proved to be insanely popular on their own.Everything Japanese only. However, there's a fan translation of the first game, released in 2010.
Cynicism Catalyst: Iku Mizushima, after the death of his twin sister, he ended up losing his trust in everyone.
Can't Hold His Liquor: Tsukiko's teacher Haruki Naoshi gets hyper pretty fast when he had some liquor. And the school nurse, Hoshizuki Kotarou, falls asleep after having too much.
Cash Cow Franchise: First Drama CDs, then visual novels for the PC (later ported to the PSP and 3DS), then an anime and finally fandiscs for each of the PC games (which were also ported to the PSP) The list of Drama CDs keeps growing.
Oblivious to Love: Somehow, Tsukiko fails to notice that 12 hot guys are in love with her.
It get worse (better?) that in After Spring, two (three?) more candidates appeared. And After Summer adds the Idiot Trio, After Autumn a bunch of Tsukiko's classmates and in After Winter finally Ophiuchus, probably with more side-characters as potential males again.
Off Model : The anime has more QUALITY than Mrs. Fields.
Twincest: Slightly hinted in the relationship between Iku and his twin sister, probably onsided on Iku's part because his sister was in love with Kotaro. He views her as the ideal partner that he already lost in the beginning.
Two Guys and a Girl: Kanata, Suzuya and Tsukiko are childhood friends ... and as it turns out, Tsukiko was also friends with Yoh as a child, although she forgot all about it.
Western Zodiac: The personalities of each original bachelor (13) are partly supposedly based on the signs' personality traits.
Yandere: Suzuya. There's a reason Tsubasa calls him Scary Guy, you know.
Specifically, in Spring, Tsukiko is given a love letter. She rejects it. The guy isn't pleased, and ambushes her later on. Kanata shows up, and if you choose to go and get Suzuya, Tsukiko will run into Yoh. The two go back to the rooftop to find Suzuya, adjusting his uniform and standing over the guy. Not to mention the constant warnings he gives her regarding his jealousy...
And then in After Spring, Tsukiko is approached by two guys. Suzuya doesn't like this, and proceeds to beat them black and blue. It takes Tsukiko begging him to stop to get him off them.
Iku. At first he's a yangire but he will eventually turn into this if you choose his route.