Mitsuharu was always a perfectly fine option, even if he is a rich brat he is abnormaly nice, he and his family is the type that even respects their servants and that tells you a lot about their characters, Satoko simply doesn't love him, and I do agree her chemistry with Shinpei is more unique, he gets her were no one else can, and she does too, but lets not forget this is basically an "I can fix him" kind of relationship, Shinpei is a mess, to the point I really can't say he was just a good guy in awful circumstances, he is deeply twisted and doesn't really respects life anymore, Satoko doesn't like that, she knows is wrong but since he is genuinely good to her (and some of his friends) she hopes he , at least , can stop for her, but that need TIME a lot of it, and Satoko lifetime isn't enough to put him in the healing path, the only way is for them was being alone together, like in the island, but thats not viable anymore.
Overall this is a mess, the mangaka knows Shinpei is a genuinely bad man and doesn't sugar coat that fact, he may be good with his girl, but a criminal with years of abuse isn't going to be good just for falling in love, he'll get worst. Satoko doesn't have it easy, is not about being smart, she is just 16 too, not even adults would be able to find the right answer to this situation, if theres even a "right answer" ofc.
Mitsuharu was always a perfectly fine option, even if he is a rich brat he is abnormaly nice, he and his family is the type that even respects their servants and that tells you a lot about their characters, Satoko simply doesn't love him, and I do agree her chemistry with Shinpei is more unique, he gets her were no one else can, and she does too, but lets not forget this is basically an "I can fix him" kind of relationship, Shinpei is a mess, to the point I really can't say he was just a good guy in awful circumstances, he is deeply twisted and doesn't really respects life anymore, Satoko doesn't like that, she knows is wrong but since he is genuinely good to her (and some of his friends) she hopes he , at least , can stop for her, but that need TIME a lot of it, and Satoko lifetime isn't enough to put him in the healing path, the only way is for them was being alone together, like in the island, but thats not viable anymore.
Overall this is a mess, the mangaka knows Shinpei is a genuinely bad man and doesn't sugar coat that fact, he may be good with his girl, but a criminal with years of abuse isn't going to be good just for falling in love, he'll get worst. Satoko doesn't have it easy, is not about being smart, she is just 16 too, not even adults would be able to find the right answer to this situation, if theres even a "right answer" ofc.