The ending made me so mad, reading the entire manga was a waste of time with no payoff and to add insult to injury it's a giant flipping plot hole. If the power they got allowed them to revert time (it shouldn't hence the plot hole) then there was absolutely no reason for the final fight to occur and the MC should have easily had the power to fix everything but noooooo, instead they decide to engage in another ridiculously stupid game. You trade blows with each other and each blow you receive you lose an important memory until you give up and don't want to continue anymore. And the bad guy gets asspull plot armour that prevents him from losing his memory over and over again until it hits that Take That, Audience! (tvtropes) sweetspot to spite the audience and kill off beefy boy.
I feel sorry for the poor bastards that read all of part 1 too only to get such a lackluster ending to the original MC but I guess that is far better than what author did to beefy boy of this sequel here. Acid Mana the pivotal main antagonist completely gets away scot-free, she also killed her brother which I'm assuming that was done because of executive meddling because the whole super power arc wasn't very well received and the author couldn't figure out a good way to finish it and move along so he just pulled something out of his ass.