So A.I. discovers emotions, knows how they can digitize those emotions, and controls humans by creating devices that traps humans in a world where they can fulfill their desires eternally, just like the matrix.
The old guy, one of the last humans who are not being controlled, wanted humans to break free from those desires. Doing that is not as easy as just unplugging the cord from humans' brains, after all. Because the humans must first break free from their own desires, otherwise they'd just escape back to those devices eventually.
The old guy then hacks into several peoples' devices. He prevents them from getting their desires fulfilled, so that they work and fight their way out to the exit. Makoto was one of those people. One by one, the test subjects fail somehow. We see that the ones that remain (still willing to escape) are people from America, China, and Makoto.
The old guy keeps an eye (no pun intended) on the remaining test subjects' worlds. He needs to constantly prevent them from getting their desires fulfilled, so in Makoto's case, he just kills Ai whenever Makoto confesses, because it's quite apparent that Makoto's desire is being in a relationship with Ai.
The A.I.s, however, knows about the old guy's plan, or at least that someone is attempting to leave their desired world, when Makoto kills the detective. So in the last several chapters, they tried to prevent Makoto from escaping by showing him a glimpse of what they (the A.I.s) think the real world is, a world where you need to fight to survive. A harsh, cruel, and flawed world.
It's up to Makoto now to stand up and man up. Humans are more than just pleasure-seeking animals. Show them that humans have what it takes to rise above total subjectivity.