In Chapter 1: Like words in the sand daily life 2, Monokuma sends out his first motive, which is giving everyone in the island lost memories about their loved ones through their dreams. While some of them are pretty funny (Taka and Mondo's shared memory dream, for example), the context makes it rather bittersweet at best, and downright depressing at worst.
Adding to that, Chiaki’s memory is with someone who's implied to be Hajime. But, since she has no memory about them at this point of time, she doesn't recognize them and doesn't understand why she feels happy with them in the dream. What makes it worse is that, if it follows canon, this would mean she forgot the first person she managed to make friends with.
Ryota has a similar case, but with the Ultimate Imposter. What makes it worse is that, due to the fic's setting, there's implication that their relationship is likely strained in the real world.
In Monokuma’s ‘revised’ motive, the students (as well as Koichi and Kyosuke) have to play an arcade cabinet with games specifically tailored to them. At the end of each game, they receive a folder with a picture of their respective loved ones. Their reactions vary.
Chiaki’s folder on the other hand, is completely empty, further reinforcing her status as a loner. Also doubles as a Kick the Dog moment.
Koichi’s reaction to Kyoko’s death. The poor guy breaks down and believes that he failed to keep his promise with Jin.
The motive of the first culprit: Hiro. It turns out that the two motives, i.e. the dream memory motive that was then scrapped by Monokuma, and the game motive had something to do with his mother. The memory was already bad enough, but the second motive only pushed him further and caused him to become desperate to leave the island in order to find out what happened to her, even to the point of committing murder. The way he becomes so desperate to defend himself during the class trial, only for him to start apologizing and begging for mercy before his imminent execution, is pitiful, to say the least.
