• This Protagonist is just so WEIRD, I can't explain the reason to make his girlfriend (Rumi) a step-sister and the way it concludes this is something along the lines: "Now you are my sister and my lover". Like why!? If the author did this to link the relationship with the title of the novel, welp, he did a bad job 'cause I didn't understand sht.
• The younger step-sister of MC is another whole thing. It appears she was thoroughly abused by her father with violence and r*pe and then went to live with Hayato (MC) and his father (don't think his name was ever mentioned at all lol). Afterwards she goes out with Hayato (despite being, again, step-brothers) and decides to cheat on him with multiple partners. Y'know, the audacity of not only cheating, if not using and mocking him as an ATM (she used the money for her cheating partners for what I got) and threatening to stab him with a knife if he doesn't forgive (?) her and then tries to kill him when she got kicked out! If it weren't for our Loli our boy would be dead 😞. And then the only thing we know about her is that she is in a Girl Rehabilitation Center for years to come.
• The out of hand revelation that Hayato was OLDER than Rumi, despite being a high schooler and the other being the step-mother of the senpai that cuckolded (?) him. And their falling in love with just an erot*c encounter is just so unrealistic, he basically coerced her into doing it and then she falls for him immediately after the act!? Even abandoning her son (from my POV of course) for someone that she just knew, met and ducked (this part wasn't clear tbh, idk if they knew beforehand but this is still incredibly s*upid). Their relationship grows incredibly fast with an equal amount of unnaturalness. Lines like: "I love you because you are kind" WTF!? She talks as if they knew everything about each other and ignores the "you took care of him so you need to take responsibility for his actions" that he coerced her with.
• The situations they end up because of Rumi are just XD. Appears Rumi's ex-husband (biological father of her step-son) in front of MC's house (son told him) to mend their relationship that grew apart cuz of his cheating, she points this and then tells him that Hayato is her new lover. Obviously, he doesn't accept because he is her brother (the news travel so fast lol) and then the pair of brother-sister kissed in front of him and he runs away. A month later, he became a serial killer because she didn't accept his attempt at coming back and Hayato with 1 month of preparation in Martial Arts parries his knife and then police came and everyone's happy 😊. Then, because Rumi has a Loli appearance she got the attention of a kid's kidnapper that has everything you would get in a doujinshi's MC bout kids, fat, ugly it appears, and the iconic dialogue "I will dye her with my color".
• Then comes Senja's (Senpai idk his name xd) ex-girlfriend and tries to be Hayato's girlfriend cuz she's lonely, he rejects, and proceeds to NOT tell Rumi cuz "she'll too shocked and cry", and this WAS IN HIS THOUGHTS, bro like 1 month together and u know everything 'bout each other. He proceeds to tell her when Senpai's ex told that she won't give up and will become his step-sister like Rumi to gain his heart and she knows this cuz he told her. Then Rumi and Hayato kissed and THE END. It literally ends without providing a conclusion to the "love" (Is just too sudden) of Senpai's ex.

I did a summary of the whole plot without purpose😕. Welp. In conclusion, every character in this novels feels one-dimentional, Akane being a b*tch, Rumi being loving towards MC for kindness idk, Senpai's ex loving MC for whatever reason and Senpai being bi and try to force himself onto MC :)