Kono Oneesan wa Fiction desu... It's a manga with great characters that started out strong, stalled for a bit, then went for a rushed and underdeveloped conclusion. Let's start off with the one I feel most divided on - Story (beginning-middle 9/10, ending 4/10): The story is pretty simple, it is just a slice of life with elements of harem and romance. The main character finds a passed out girl on the side of the road, gets in a ecchi situation, and learns later that she is his mother's (a mangaka) assistant. He teaches her about her job, she gets a crush on him, characters from hisschool are introduced... and that's about it for the story, with the exception of the ending.

The ending was a rushed ending, and I personally found it very unsatisfactory. Without spoiling it too much, I will say that relationships remain mostly unsolved, the canon pairing was weird, and it felt like they were trying to tie up loose ends by serving it as a sort of spaghetti.

Now for the first of the nice categories - Art (8/10):

Art was good, not exemplary, but I never looked at anything as "off", and everything looked like what it was supposed to, though I never had a "wow I love that art" moment either.

Character (9/10):

The characters were what made the story. The main character is a confident and mature high schooler, contrary to so many other harem leads. He's not boring, nor overly comedic, and he often acts as a straight man, while still maintaining his own personality. Every girl in his class likes him, whether romantically or as a friend, to the point of him getting valentines chocolate from all of them. However, he leans towards the side of being oblivious about anything love related. The attempt of the author to solve this is about 50% of my grudge towards the ending, as it was 2 chapters of character development that came out of the blue and seemed unrealistically forced.

The main girl for the majority of the story is his assistant. She is an attractive, dedicated, and intelligent young women, but she has several flaws. First, she is terrible at alcohol, and will use the main character as a pillow to sleep with if she gets drunk, and second, she often leaps to conclusions, despite there being not enough info to fully conclude that. However, she is a loveable and interesting character. She quickly gains a crush on the main character; but alas, the manga never fully goes all the way with this, another of my main faults with the ending.

The other major girls are primarily 2 of his classmates. The first is a small shy loli who also jumps to conclusions, and she had a crush on the main character since the first chapter. Unfortunately, he character remains able to be described in a single sentence for the entire manga, and is my candidate for most boring girl.

The second girl is a much more interesting character, in my opinion. She loves to tease the other girl and is generally a playful and fun character with a good sense of humor. Early on she seems to develop a crush on the main character; however, the author seems to have forgotten that, as she doesn't show much signs for the rest of the manga. Despite being an interesting and likeable girl (and personally my vote for best girl), she never gets much character development, primarily being a sidekick for the loli, and rarely getting moments for herself.

Other characters drop in from time to time, but most of them have their own relationships and are basically side stories, so the harem pretty much remains at 3 relevant characters. However, each and every one of them is an amusing and interesting character.

Now, the most important field - Enjoyment (8/10):

I would give the beginning 10/10 for good character introduction. I would give the middle 8/10 for keeping my interest. I would give the ending 2/10, for one of my least favorite endings of all time, and would recommend you stop reading as soon as you see definite pairings being established (excluding for minor characters), as it just goes downhill from there.

Overall, 7/10, a great manga ruined by a terrible ending.