The Attack on Boruto
Ever since the first chapter of Boruto: Two Blue Vortex manga, fans have noticed how Mitsuki has wanted to kill Boruto. His bloodthirst was so evident that even Kawaki had to ask him to calm down. Subsequently, the Boruto: Two Blue Vortex chapter 6 spoiler saw Mitsuki attack Boruto. But why did Mitsuki attack him?
The previous manga chapter saw Sumire and Sarada learn that Amado was having doubts about his memories. As they were trying to think up a piece of evidence to help confirm the memory manipulation, Boruto returned to the Hidden Leaf Village and reunited with Sarada and Sumire.
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The Revenge of Mitsuki
As fans might remember, Boruto: Naruto Next Generations manga ended with Eida using her Shinjutsu to switch Boruto and Kawaki's places. Before that, Kawaki sent Naruto Uzumaki and his wife Hinata to an alternate dimension. Additionally, he attempted to kill Boruto to get rid of Momoshiki Otsutsuki.
Kawaki and Eida as seen in the manga (Image via Shueisha)
Hence, after Kawaki got Eida to use her Shinjutsu, everyone, including Mitsuki believed that Boruto was the outsider and Kawaki was the Seventh Hokage's son. With that, Mitsuki who thought of Boruto as the 'sun' to his 'moon,' believed that Kawaki was his 'sun.'
Mitsuki preparing to fight Boruto in the manga (Image via Shueisha)
Additionally, Kawaki also forced Eida to misinform Shikamaru that Boruto killed Naruto and Hinata. Thus, Mitsuki was led to believe that Boruto not only tried to kill his 'sun' Kawaki but actually managed to kill his parents Naruto and Hinata. Thus, from Mitsuki's perspective, Boruto was life-threatening for Kawaki. This was the reason why Mitsuki attacked Boruto in Boruto: Two Blue Vortex manga.
The Obsession of Mitsuki
Mitsuki is not a normal human being, but a synthetic being created by Orochimaru. Thus, Orochimaru wanted his son to choose a path of life for himself. But in the beginning, he pushed Mitsuki to befriend Boruto and carve his own life choices. This development saw Mitsuki accept Boruto as the 'Sun' to his 'Moon.'
Boruto and Mitsuki as seen in Boruto: Naruto Next Generations (Image via Studio Pierrot)
Considering how the moon cannot glow without the sun, it was very clear that Boruto was very important to Mitsuki. This saw Mitsuki risk his life for Boruto on multiple occasions and use his power up - the Sage Mode to fight enemies who threaten Boruto's life.
Unfortunately, following the effects of Eida's Shinjutsu, Boruto and Kawaki's lives got switched. Thus, Boruto was no longer Mitsuki's 'sun' but it was Kawaki. Considering that Boruto threatened Kawaki's life and 'killed' his parents, there was no way that Mitsuki could calm down. Therefore, he wanted to kill Boruto to eliminate the one person who threatened the life of his 'sun.'
Unfortunately for Mitsuki, he could not kill Boruto at the end of Boruto: Naruto Next Generations, and instead had to wait for three years, i.e., until the beginning of Boruto: Two Blue Vortex manga. By this time, Mitsuki's will to avenge his 'sun' had developed into a bloodthirst that was very obsessive and nearly uncontrollable.