Second season of Infinite Stratos.

In their teenage years, few things can hurt people more than the heartaches that come with unrequited love. Such is the case for Natsuo Fujii, who has found himself entranced by his school's ever-cheerful teacher Hina. Deflated by this unreachable desire, Natsuo humors his friends and attends a mixer. There he meets Rui, a girl whose lack of excitement rivals that of himself. After bonding over their mutual awkwardness, Rui takes Natsuo to her house and asks him to have sex with her, hoping that the experience will stop her friends from treating her like a clueless child. With his hopeless feelings towards Hina still on his mind, Natsuo hesitantly agrees. Equally unfulfilled by their "first times," the two decide to part ways as strangers. However, before he even has a chance to process this experience, Natsuo's father drops a major bombshell: he is getting remarried, and his new wife Tsukiko Tachibana is coming over now to meet Natsuo. As if that was not enough of a shock, her daughters—and, in turn, Natsuo's new sisters—are Hina and Rui Tachibana, the woman he's in love with and the girl with whom he shared his first night. Now, Natsuo must come to terms with the feelings he has for his step-siblings as his eyes open to a darker side of love. [Written by MAL Rewrite]

Famous for his military service in the 39th Asian War, the legendary Swiss robot Montblanc is violently murdered. Humans and robots around the world mourn for the beloved celebrity. Montblanc's popularity only grew in the years following the war, thanks to his dedication to nature conservation and his loving personality. Once a fellow war veteran, robotic Europol detective Gesicht is sent to investigate Montblanc's tragic demise. In his pursuit, Gesicht uncovers evidence of a mysterious entity known only as "Pluto." He also learns of a conspiratorial plot to dismantle the eight specialized robots from around the world who participated in the war. Racing against time to save those who still remain, Gesicht grapples with his memory, morality, and a world full of hate, desperately attempting to defend the fragile coexistence of man and machine.

A world where it has been established that people routinely swing between slightly different parallel worlds... Koyomi Takasaki, who lives with his mother following his parents' divorce, enrolls in a local university prep school. Due to the atmosphere concentrated on studies and his social awkwardness, Koyomi is unable to make friends. One day, he is suddenly approached by his classmate Kazune Takigawa, who tells him that she has travelled from the 85th world where she and Koyomi are lovers.