A shounen story where 2 teenagers went back in time to the "Three Kingdoms" period of China. An entertaining action series with some light moment & a bit of romance. You also get to learn a bit about that era.

From JanKenPon:
Middle schoolers, Shiro and Masumi, encountered a mysterious dragon that brought them back to the time of the Three Kingdoms; situated in ancient China. As soon as they arrived, they were rescued by the Han Kingdom. Not long after these events, Masumi was kidnapped and Shiro barely escaped death... Soon the story gets more complicated as they are stuck in the past.

In 1997, Ryuurouden won the Kodansha Manga Award for shōnen manga.

Rinosuke's useless and vagrant father is now dead. Now, at the age of 16, he is completely alone and will have to quit school to make ends meet. On the night his father dies, a naked woman with large breasts falls from the sky and lands on top of him. She introduces herself as Sakamoto Marina, the future wife of the future Rinosuke. She states that she used a time machine to come back to the past, and start a new life with the younger Rinosuke. Rinosuke's new life with his future(?) wife begins.

At age 33, I am a loser, jobless and virgin, who only has remorse and pity for myself. Called by Anna, my secret crush in my childhood, and her fiance, I come to face the reality. But after I fall from the roof (caught wearing a grade school girl's swimsuit) I find myself to be back in the past. Now I will get my life back.

From: Easy Going Scans
As a result of a strange encounter with a mysterious carcinogenic fetus he found inside a patient’s skull, brain surgeon MINAKATA Jin has slipped back through time. Equipped with modern medical knowledge, he faces various fatal diseases and injuries. Then, he meets the ordinary people of Edo as well as illustrious figures, and his surgical knife carves out a new history and story of life.

Note: Won the Grand Prize at Tezuka Osamu Cultural Prize in 2011.

Released in English by the Artist on his Patreon:
https://www.patreon.com/motokamurakami

Feeling rebellious toward his overprotective and neurotic mother, 16-year-old Souma Mitsuya cares only about his violin and his hospitalized grandfather. On the night his grandfather's condition suddenly worsens, an earthquake hits, and Mitsuya finds himself lost and alone in Japan of the year 1921.

Struggling manga author Satoru Fujinuma is beset by his fear to express himself. However, he has a supernatural talent of "noticing things" that forces him to help people.

Boku dake ga Inai Machi Gaiden