Kono Naka ni Hitori, Imouto ga Iru!

An aggressive harem comedy with heavy focus on ecchi elements such as frontal nudity and breasts, suffering from shallow characters with occasionally shameless behavior. Thus the "secret younger sister" plot, together with an interesting male lead who has to stand his ground against a conspiracy within his own future company, is the much more interesting layer with lots of story twists and hidden agendas - is there anybody who can be trusted? This scheming and machination element alone made this series worth watching for me as a mystery show following the given clues, whereas the romance component failed to convince me.

• Episode 01: (0-) Shougo is fair game right from the start, with two girls attempting to kiss him already. The cliffhanger makes me wonder: Why would they let that nice idea go to waste at this early stage already?
• Episode 02: (0+) Four ecchi scenes (all including breasts, including frontal nudity), but otherwise a decent episode, introducing three more girls and giving Miyabi something to think about. And Shougo is quite the ladies' man, unlike those many clueless wimps in harem anime. "Mr. X" was another nice add-on, and it's good to see they do know about the existence of DNA tests, i. e. they're not all stupid.
• Episode 03: (-) An orgy of embarrassment due to a simple unresolved misunderstanding, causing two slutty girls to try and "cure" Shougo. The surprising twist at the end doesn't save this episode as it's based on a mere assumption.
• Episode 04: (++) A huge step forward in terms of both story and character development for two lead girls, answering significant questions and posing new ones at the same time. And yes, the "KyoAsu IMT-270" cellphone does play a core role in this story, even more so now that we know who constructed it - there's still trouble ahead for its owner.
• Episode 05: (0+) This one had a slow start (why doesn't Shougo just switch off his cellphone at night?) but the second half had us return to another character's story and one more clue from the cellphone department.
• Episode 06: (0-) Similar to the previous one but much weaker, with a strange focus on a side story and an unconvincing explanation by the culprit. And shouldn't Shougo start asking his lead girls for voluntary DNA test samples by now, and then focus on the "cleared" ones?
• Episode 07: (0-) The first DNA sample, at long last. The fourth girl's arc begins but her agenda appears weird: If she wants to remain unknown then why announce her existence to the public? And her access to that special cellphone was all too random. Downgrade for "Characters" due to no progress on the "girlfriend frontier".
• Episode 08: (0) The fourth girl's agenda was a nice twist, and her explanation was plausible. The positive aspects were outweighed by fan-service elements and a growing harem of one-dimensional girls though.
• Episode 09: (0-) A new girl moving in next door to Shougo's apartment, a new story twist, and the first DNA test results. Despite the shallow characters, the "sister mystery" still holds my interest.
• Episode 10: (0+) The first contender places her final bid. But it's much more exciting to see how close to Shougo the enemy forces have placed their agents already, as not even the DNA test result may be trustworthy now.
• Episode 11: (+) More evil machinations, finally a date with an unexpected girl, and the second baddie being clearly identified, so almost no time for ecchi filler material. Will one episode suffice for answering those many open questions?
• Episode 12: (++) Walls of text, but a plausible and detailed explanation about what was going on in this series and who had which hidden agenda. Don't expect a harem winner though.
• Episode 13 OVA: (0) A dating competition. Starting with perverted delusions of Shougo, only the last contender understands what this event is actually about, learning from the previous mistakes of her rivals.