Amakusa 1637 is a 12-volume josei manga by Michiyo Akaishi, published from 2001 to 2006 in Shogakukan's Flowers magazine. It follows the adventures of six Japanese teenagers: Natsuki Hayami, Masaki Miyamoto, Naozumi Yatsuka, Eri Kasugano, Seika Akishima and Eiji Horie. They're classmates from a Catholic school in Kobe, and they barely survive the Great Hanshin Earthquake of 1995; five years later, during a school trip to Nagasaki, they get mysteriously transported... to the Amakusa region in the year 1637, shortly before the historical massacre of the Christian population.Having been transported to different times, the six kids first must reunite with each other and assess their current situation, as well as what has changed between them since some arrived to a time set prior to the others's arrivals. And when they're done with it and gather their common knowledge of the future, they set out to exorcise their own inner demons as well as to prevent the carnage...This manga contains examples of the following tropes:
Action Girl: Natsuki is a Kendo expert and the sister of a Heir to the Dojo. Said abilities come off VERY handy when she's mistaken by a local swordsman.
All-Loving Hero: Natsuki's greatest strength is her ability to unite others behind her through sheer kindness.
Body Double: Basically, what Natsuki is to Shirou. She's at first mistaken as him, then she must keep up the charade to protect the people and avert the Shimabara Rebellion because the real Shirou is Dead All Along.
Downer Beginning: The manga starts in 1995, with the junior-high-aged Natsuki and Masaki barely surviving the Great Hanshin Earthquake that decimated their city, Kobe. In-story, said 'quake actually was caused by the same phenomenon that would throw the kids in the past six years later.
Drowning Pit: Matsudaira, the lord of Shimabara, has one in the grounds of his castle. At some point, both Kichou and a local girl named Yone are locked in it.
The Dulcinea Effect: Jahn saved Seika's life when she arrived to the past and fell for her. She doesn't necessarily reciprocate, though.
Identical Stranger: The Bifauxnen Natsuki looks a LOT like Shirou (only younger and female), and this is a BIG plot point since the people believe her to be either Shirou or an angel that took Shirou's form to help them.
Maybe Magic, Maybe Mundane: The locals believe the time-travelers to be messengers from "Deus". The time-travelers are a lot less certain, and know that their "miracles" have mundane explanations, but some of the coincidences are troubling...
Meaningful Rename: Seika is also known as "Mariana", her Christian name. Natsuki is first referred to as "Francisco-sama" and later as Shirou. Naozumi is renamed as Kotada... and Masaki, as Miyamoto Musashi.
Mission from God : Seika is confident the group is on one. Her confidence isn't necessarily shared.
Mundane Afterlife: Inverted. At one point, the locals ask the protagonists to describe the "Heaven" they believe they come from. When the protagonists comply, they are themselves shocked and moved when they realize the modern society they describe - one of electric light and heating, religious tolerance, rule of law, and ample food - is, in fact, Heaven for the medieval peasants. A paradise that they'd been taking for granted.
Romantic Two-Girl Friendship: Eri and Natsuki. The first openly says that, had the latter been a man, she would be head-over-heels in love with boy!Natsuki.
Saintly Church : The protagonists seem to be forming a proto-example of this.