I seem to have a knack for picking out incest manga based on the cover. Nieruchi - which roughly translates to "boiling blood" in English - is one crazy ride with enough drama to keep you interested and entertained, but hardly makes you feel anything akin to that of the suggestive title.
Sera and Rumina are half-siblings with the same father, George(?). George was married to Rumina's mother, but cheated on her with another woman which resulted in Sera's birth. The story opens with the two mothers having a friendly tea session together, and it baffles me that the author never provided more back story about
the affair, or the fact that the two women seem to be on good terms and completely okay with their man's infidelity, so much so that they allowed their kids to have play dates together and become besties. Is this a regular occurrence in Osaka (or wherever the manga is set; it seems to contain quite a bit of Kansai-ben)?? But anyway, fast forward some ten years. Now both in secondary school, Rumina has a crush on Sera, and she becomes intimate with a male classmate out of desperation to escape her feelings. It's never made clear why she's so hung up on Sera like he's the only guy in the world, apart from that one time they held hands when they were 5-years-old. And Sera, too, has a pursuer, but she reminds him of his helicopter mother and it makes him quite repulsed. He tells Rumina that he's afraid of all women except her, and they share a kiss. The logic of how they came to fall in love with each other doesn't seem convincing, but I guess I'll give them the benefit of the doubt and read on. A series of unfortunate events happens, and the two become separated until a chance encounter in adulthood, and from there the story dovetails into a romance between any two young people with occasional allusion to their blood relationship almost like it's an afterthought of sorts.
My main gripe is that the nature of their relationship was not properly dealt with at all in the story. From the beginning very little is revealed of Sera's inner thoughts, and initially he seemed to me motivated more by spite than by love, which makes his character growth later on in the story somewhat abrupt and unrealistic. Rumina, for all her desperation and awareness of the "wrongfulness" of her feelings, doesn't put up much of a fight, both externally and internally. She seems to give into Sera's desires at will. Even after a 7-year absence in which they were both presumed to be out of each others' lives for good, there is no satisfactory segue leading up to the rekindling, no thoughts or conflicts over the moral implications of their actions. The motif of blood line runs throughout the story as constant references to a "stirring", "flowing", "simmering/boiling" within their veins with no clear connection to any other part of the story and seems to serve no purpose. The parents are spectacularly useless (or just too good at removing themselves from the picture) and, for the most part, one-dimensional characters with no real depth. We never get to know their thoughts on the affair and its consequences on the kids.
The sketchy art style lends an overtone of grittiness and intimacy to the story, but some details are skipped/glossed over here and there that caused some little confusions, especially towards the end. Overall, I feel the manga suffered from poor pacing, trying to cram a story spanning 20+ years into a 7-chapter volume, especially one dealing with a delicate topic like incest, feels way too rushed and there's simply not enough room for insight into characters or buildup leading into events. While not a must-read, this is still a refreshing break from the typical high school romance with a satisfactory conclusion.