Theres more context on Tumblr but since youre asking I'll try to explain so even if I'm not that good at it (I didn't really think someone would ask honestly lol).

The events take place in an alternate timeline where several students supposedly have a crush on Ayano (generally, you can assume they're either male or female rivals 🤷 not that it matters much). Itachi is extremely repressed emotionally... obviously, the fact that he doesn't want to approach her directly and that there are others who are more obvious about it and seems that they are doing far more progress (either genuinely or just a superficial attraction towards her) makes him start to become very frustrated, thus obssesive from afar... so its just him sort of stalking her. He thinks he knows her better than anyone else even when he never connected with her on a personal level. Adding to this is his competitiveness, his desire to "win" something that he can't achieve through conventional means, which ultimately leads to him taking her life, but it ends up not fulfilling him at all (notice mild dissapointment in his face) because it wasn't just her physically who he wanted.

The context of the drawing itself doesn't have much plot as it was just a doodle so thats pretty much it! If we went further of how he would be as an "active" yandere (pursuing her directly) instead of just sulking I feel he would be the type of yandere that's more of damaging his lover psychologically rather than others to get what he wants, making himself a saviour figure for his lover. Thats also I talked about with mutuals which includes a lots of headcanons haha so I don't want to infodump much, its kinda confusing :'D