First of all, if you don't like tragedy, sensitive to disturbing components, don't enjoy psychological series in general.. My advice would be that you should not read this. This is not a manga that everyone would enjoy. So please do not say things like "gosh who would kidnap to plant life in someone" like duh the characters in front of us are kinda not okay in the head.. And it's not written in the best way anyways.. (I want to cry) This manga is the prequel, and has a second volume as sequel. This is the first one you should read. The startis interesting, that should be interesting for everyone i say. But the rest is... Yeah, no. Most would be disturbed. After the interesting start it could be disappointing.. Because the story becomes like "oh hi, from here onwards Stockholm Syndrome presents!". But the thing is, even if it goes the Stockholm way, the first volume's art does not give the usual "after Stockholm romance" vibe. The art is still solid. The art does not allow us to think that this is romance. It makes you know that the thing happening is actually disturbing, and it is portrayed just that way. The art is not romanticizing.
About the characters, they were living good but the life was not kind to them. They are traumatized middle aged men. They are not easy to change and they heal slowly. So as we learn their histories, more like the victim's history in first volume and kidnapper's history in the second, you empathize with them. No, you dont normalize them. You don't start to think that it makes their actions right. You just understand them.
Anyways, this is not the best psychological yaoi you could read but i think it's worth giving it a try. It is good! This also has a movie! Both are enjoyable but if you ask me, the movie is way more disturbing. And the second volume is not really like the first volume, so don't expect horror in the next one. It's heavier in emotional way, the second volume. Anyways, go read this folks.