Not necessarily Nezchan, those two definitely are Yandere, it don't really need to always have violence, the most basic characterists of a Yandere is that they love a person and are really possessive, obssessive and territorial about them, alternating between a loving and caring side and a more psychotic or crazy side, they don't always need to stalk, confine, threaten and use violence, but that's the cliche so most of the time they do all that, but some are not violent, takes away the violence and Akki and Shouko would probably be like Koharu from Koharu no Hibi(it's het but good) that is one of the most passive and harmless Yanderes ever made, Akki is more like the classical Yandere that uses violence any time she thinks there's someone/something in the way of her love as except for chapter 4 she's always the first to attack, while from some of her dialogues Shouko seens to be more of the "I want to lock you up and never let you go" kind of Yandere, and about not using violence against others, some Yanderes are more "if I can't have you no one will" type and attack the person they love instead of others.
Nez, I love ya girl, but I think this one's got the right idea. Due to obvious circumstances, people think that yandere is synonymous with dangerous and unhealthy for a relationship. Yandere is supposed to just mean that you're crazy obsessive...so when Akki is crazy obsessive for Shouko to devote 100% of her attention to her, Shouko is crazy obsessive for Akki to want her 100% of the time. Under 99.9% of the circumstances, those characteristics lead to unhealthy and stupid bad relationships. But these two found each other and found that .1%.
Of course, it is also very arguable to say that since language is, at its roots, just a slur and gaggle of sounds humans make to communicate a message, the connotative and colloquial meaning of yandere might be more correct a definition than the literal word-for-word denotative one. But that's arguing semantics and ultimately just digresses from the main point here.