"Can't deal well with stress."No offence either, but relationships with age difference of 15 years do happen in real life.
Speaking of Hayashida and Shimada as potential partners for Akari, Rei did discuss this at some point in his monologue chapters ago: Hayashida is sincere and can be Akari's anchor when she's lost, but his income as a teacher is low, while Shimada may tickle Akari's motherly tendencies and habits and can support her dreams financially, but can't deal well with stress.
Also, there might be another character getting into the picture later.
And in the end, it depends on how Akari feels about committed relationships.
This was addressed the first time they met, and it's the opposite. Just as something simple as eating her food made his stress-related stomach pains go away. It's less her and more on Shimada, you know, letting himself be loved and supported.
Akari and Shimada are uniquely situated in sharing similar fates of sacrificing their lives for a greater cause and being able to share the burdens the other bares.