As readers we know that Yuuto has some supernatural power of coercion and as he controlled her to commit suicide, it is essentially murder.
However of course, that would be impossible to prove in court. To consult precedent, he'd be convicted of promoting a suicide attempt, which is a class E felony in my state or involuntary manslaughter either under charges of criminally negligent homicide (class E felony in my state) or second degree manslaughter (class C felony in my state). The most famous case on coerced suicide is probably this one.
Yuuto's wording is a little ambiguous, but he could still be convicted of criminally negligent homicide for being aware of Hiro's intentions and making no move to stop her.