Passage to Tokyo — Poppy Kuroki

In the second book in the Ancestor Memories historical fantasy series, a young woman finds herself back in 1920s Tokyo as Japan enters a new and dangerous era -- and a deadly tragedy awaits her city.

Yui Sanada struggles to raise her twelve-year-old brother, Hiro, while contending with the antics of their 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 traveled back through time to 1923. As feelings between the two women develop, Yui and realizes it's just weeks before the devastating Great Kanto Earthquake will happen, killing tens of thousands and leveling the city. Will Yui be able to find her brother and save her new family from the coming disaster?