Manga Like Jacaranda

The metropolis of Tokyo was devastated overnight—not by a massive earthquake or a tsunami, but by a single giant tree: the jacaranda! People—one after another—perish, trapped beneath the rubble of collapsing buildings or in the spreading sea of fire. What on earth was given in exchange for this hellish scene of screams and wailing…? With the metropolis on the brink of destruction, what should the survivors focus on, and what actions should they take? No—before that, when everything is lost, what should they choose? What is the answer???? (Source: Seirin Kogeisha, translated)