A Yandere's traits were: lacking empathy, possessing a strong desire for possession, knowing how to disguise themselves, and usually having childhood trauma. They were prone to becoming single-minded and going to extremes, yet also had an exceptionally fragile side that could shatter at the slightest touch.
That was what Shinji knew about Yanderes, and he also knew something about how to treat them.
That was, to redirect their attention so they could gain more happiness and satisfaction from other, gentler activities.
Understand the source of their emotional knot, guide and hint at them through words, and let them slowly release their stress and learn to face their own hearts.
No matter how ill a Yandere was, they were still human and had a vulnerable side. As long as the "doctor" was patient enough, they could still be cured.
Although there was a major problem before Shinji right now—the cause of his little sister's illness was himself—for Sakura's sake, it would be better to slowly begin guiding her first.
After all, the inner hearts—or rather, the vulnerable sides—of Yanderes who had no friends to confide in were harder to heal than ordinary people's when hurt, and suffered even more.
Then it would repeat in a cycle, and the condition would worsen.
If there was never a proper way to guide them, they would stay sick for the rest of their lives. Shinji did not want to see that happen.
"Tomorrow, I should ask Mitsuzuri and the others first. After all, they're the only ones Sakura is familiar with right now..."
At that moment, in Sakura's room, she was bent over her desk, seriously fiddling with bottles and jars filled with liquids of various colors beneath the desk lamp while intently writing something in her notes.
The Magecraft book on Sakura's lap,