Passage to Tokyo by Poppy Kuroki

A young woman finds herself transported back in time to 1920s Tokyo just as Japan enters a dangerous new era.

Yui Sanada struggles to raise her twelve-year-old brother, Hiro, while contending with a neglectful, alcoholic mother. During a trip to Ueno Park, Hiro runs away from his sister into a strange passage beneath a samurai statue. Yui chases after him and soon finds herself in a Tokyo far removed from the familiar world of 1995. 

When Yui emerges from the tunnel, she cannot find Hiro but meets a young woman named Chiyo and her family and learns she has travelled back through time to 1923. As feelings between the two women develop, Yui realizes she has appeared  just weeks before the devastating Great Kanto Earthquake, a terrifying event that will kill tens of thousands of people and level the city. Will Yui be able to find her brother and save her new family from the oncoming disaster? 

And if she does find her brother, will he be the same boy she lost in 1995?