For the readers who dislike even just a tiny bit of angst, I advice that you pass this manga. However, for those who feel up to it, enjoy the craftiness of the story. The plot per se is not dripping with melancholy, but at some parts, it can be a real tear-jerker- although not enough to give you puffy eyes afterwards. ;P
I've always wondered how 'falling for the enemy' would end like, especially an 'enemy' motivated by revenge. This story gives one of the best endings for revenge-themes(excluding fluff and PWP types)- not ending in a tragedy, but still retains a touch of reality, without the avenger giving up his vendetta halfway though the story.
I especially love how Ryouke's true feelings towards Aikawa were obscured until a few pages after the final climax of the story(revealing of the photos). Even then, you would have to keep on guessing whether he has actually fallen for the hero, or was still just carrying out his revenge. Thankfully enough, he clearly states how he feels about Aikawa- and thus removing any speculation on his real motives.
As for Aikawa, it really is sad how he ended up in such a miserable state of 'kindness'. His reaction was most reasonable though, for someone who experienced abuse and was not able to go through psychological therapy, as such, he lived most of his life under the feeling of torment for his supposed 'faults'. The agony of self-accusation caused by his experience of abuse, thus made him feel compelled to keep on searching for forgiveness- his only means of salvation from the guilt eating at him.
Being the recipient of hatred and abuse from everyone around him, and him just allowing them free-reign to ruin his life, might make him appear weak-willed, but that is not it. It is his way of obtaining atonement for his sins- for his grave sin, the one which ultimately triggered his downward spiral. Nevermind whether he really was at fault or not, he would seemingly 'gladly' receive the blame for almost everything and do his best to atone for it, even at his own expense- a result of his trauma. Through these things, he is able to keep his sanity and maintain the will to live.
Understanding, forgiveness, and love play a great part in the conclusion of the story. How it was interwoven so that its(Aikawa's atonement) development would be subtle, yet have an undisputed conclusion made it a truly great read.