BTOOOM!

Tyrannos Japan views Ryouta and Nobutaka as they continue their fight but Ryouta is able to anticipate Nobutaka's strategy, and chooses to retreat, leaving behind the cashe of food and BIMs. As Nobutaka leaves he realizes that he knows Ryouta, leaving Ryouta to wonder how Nobutaka knows his name. When they return to Kiyoshi, Ryouta has a flashback and it dawns on him that Nobutaka was in fact, his best friend back in high school. However their friendship met an end after Nobutaka slept with Ryouta's crush. Soon Masahito decides to betray Ryouta. Ryouta, Himiko and Masahito then head back to the abandoned building where Shiki stays, to find medicine for Kiyoshi. Masahito then finds some expired medicine and puts them in his case which he entrusts to Ryouta, who has the realization that Masashi was right about him being too trusting of people. When Ryouta signals Himiko, she comes running back and shouts at him to drop the case because Masahito placed a hidden BIM in it just as it detonates. (Source: Wikipedia)