Chapter 48

A Time for Action (実行の時間, Jikkō no jikan) is chapter 48 of the Assassination Classroom manga.

Short summary
Korosensei rushes frantically to rescue the students as they're getting swept away. Karma appears, finding the pool drained away and Terasaka petrified at Shiro's change of plans and what had just happened. Terasaka frantically tries to shift the blame from himself, but Karma does not sympathize, claiming he'd be guilty of mass murder without Korosensei and tells him to think of something instead of pointing fingers. After Korosensei finishes rescuing the students, Itona finally appears and drags him into the water, thus beginning their second battle. Left alone, Terasaka thinks of his past and how he used to bully others to build his life, only to have it turn around once he moved into private school, with working hard and studying becoming the norm instead of skipping class. Thinking he'd eventually be manipulated by the powerful, he'd escape to class 3-E to assert his power, only to have Korosensei come and take it away again. He comes to the conclusion that up until this point, he's still being manipulated all along by others with visions and plans. With Korosensei in trouble after losing his protective mucus from the pesticide and having his tentacles weakened by the water and chemicals, on top of several students, especially Hara, still in precarious danger, Terasaka comes to swallow his pride and asks Karma for a plan to help Korosensei.

Long summary
With the class getting washed away to their deaths, Korosensei rushes frantically to rescue them. He wonders who blew the dam up and why as he goes to rescue the students. He spots a steep rocky area beyond the edge of the pool, where the students are about to plunge to their death or drown. Staring at his fake gun, Terasaka is terrified about the unexpected change of plans. Watching the soon-to-be massacre at a distance, Shiro notes that the students' bodies can't handle being saved at Korosensei's mach 20 speeds, and as such, his body will gradally absorb water as he carefully rescues the students. Itona realizes Korosensei's body could handle the water better if he could release his mucus. Recalling from earlier, Shiro agrees in that Korosensei can coagulate the water to maintain osmotic pressure, pointing to the pesticide as a way for him to exhaust his mucus, thus forcing Korosensei to lose speed as he rescues the students.

Karma appears, noticing the pool having swept itself away. He then spots Terasaka, still petrified at Shiro's misinformation of the plan. Realizing the seriousness of the situation, Karma pieces together that Shiro and Itona have just used him. Spotting Karma, Terasaka grabs his chest and frantically tries to convince him it wasn't his fault, that the two of them set him up. Before Terasaka rambles on, Karma punches him and scolds him for the fact that without Korosensei able to move at Mach 20, he'd be guilty of mass murder, and that's it not anyone's fault but his own. Leaping down the rocks, he tells Terasaka to use his time thinking with his head on what to do about the situation instead of pointing fingers. Terasaka is left sitting alone.

Finally rescuing Yoshida, the last one swept away by the water, Korosensei feels a tentacle wrap around one of his own. With the former finally pulling Korosensei into the water, Itona and Shiro finally appear to meet him. Shiro reveals that the chemical Terasaka poured earlier is an ingredient specifically designed to weaken his tentacles' movement. Itona psychotically challenges Korosensei to see who's stronger.

Trying to get himself together, Terasaka starts to think about his past, always having used to think of himself as strong. He recalls having not fought much, but because of his loud voice and large build, managing to bring weak-looking peers under his control in elementary school, his way of making a place for himself. Still being able to study, he chose to go to a private school without thinking much, as he'd thought he could continue his way of life. He recalls pressuring a student into skipping class and going to the convenience store, putting his hand on his shoulder. The student hesitantly refused, pointing that he needs to review for his English class, to which Terasaka claims it wouldn't make a difference if he skipped one class. Suddenly, Terasaka hears an insult, calling him a monkey threatening a human, and before he knows it, the rest of the class is studying. The student in front of him flatly tells him that no one skips class like him, and that being a bully pretending to be smart will only make him unconditionally weak unless he actually studies. Realizing Terasaka's grades are at the bottom of the class, the student slaps Terasaka's hand away and laughs at him, anticipating the day he could throw stones at him once he drops into class E. With Terasaka becoming the laughing stock of the school, he'd realize his shoddy weapon would become useless and that this would be the rest of his life, where students like him who take effort in changing their future would rule over those without a plan like himself. Figuring this, he'd drop to class E where he'd still live comfortably and aimlessly with everyone else, only to have Korosensei show up to give everyone a real purpose to their lives. Back to the present, he realizes that even in class E, he can still be manipulated by people with goals in mind.

As Korosensei continues to fight Itona, he realizes Itona had gotten fast and stronger than before. Shiro explains that he eliminated some of Itona's tentacles so that the remaining ones can have better power and speed. With Itona peeling and eating a banana, Shiro notes that Korosensei, in contrast, has now been soaked and his movements have become dull, to the point even his "heart" will be killed. On a cliff, the students are left spectating the battle between Korosensei and Itona. Okajima realizes the two have set them up, while Kataoka still thinks the match is unfair, with the two overpowering Korosensei on a large handicap of water. Terasaka emerges from the bushes behind the students and claims it's not just the water, but that he also rescued them. He points to some of the students still being left in unsafe areas, especially Hara, with her chubbiness, hanging over a branch about to break. He credits Korosensei dividing attention between the battle and the students' safety as a losing factor, also planned by Shiro. From behind him, Maehara yells at him not to say it so thoughtlessly and starts to suspect, along with the rest of the students, that Shiro manipulated him. Confirming their suspicions, Terasaka laughs and openly admits to having been manipulated as a guy with no vision. He then determines to take control of the situation, having lost trust with the pair and not caring anymore about the reward money. Pushing Karma's chest, Terasaka asks him for a plan. Karma complies, but first asks Terasaka if he'll be able to carry it out, as he might die. Enthusiastic and rushing in, Terasaka affirms that he will, as primary offenders who get results. Karma teases him in that he still hasn't thought of a plan, to which Terasaka is left frozen in embarrassment.