Mugen Kairou 1 + 2

Although two eroges would generally warrant two separate reviews, even if the games are sequels of each other, Black Cyc's Mugen Kairou (2005) and Mugen Kairou 2 ~Rasen~ (2009) are so closely related that one cannot discuss one game without referring to the other. This review will not discuss Mugen Kairou 1.5 (2009), as I have not played it due to it originally being a Cyc Members only product. It also received poor reviews, and was written by a different author, so I am still likely to ignore it if it is made available on dlsite or elsewhere.
As both Mugen Kairou's are loop games, it is difficult to give a description of either story, both because the perception of certain events will drastically change as more information is provided, and also because the stories of both games are closely intertwined. Both games involve a protagonist 'Taro', who comes to live in a mansion with four sisters (and 'Shiro' in 2, along with a few other characters) as a 'katoru', or pet of sorts. The sisters take responsibility for training 'Taro', in events known as 'ippu'. The player selects which sister to receive the 'ippu' from, as shown on the image below. At first, all of the days are 'red', but on later loops, many change to 'black' providing either different events, or darker versions of the same event. After an ending is reached, the game will loop back to the beginning, with their being 8 loops in total, almost all of which provide further information about the main story thread. The relationship between the two games is left unanswered, although notably, Black Cyc changed all of the seiyuu between Mugen Kairou 1 and 2, despite the games sharing a number of characters. I see 2 as an 'answer' of sorts to 1, both because 1 was made prior to 2, and the scenes that are common to both eroges generally have slightly more information provided about them in 2. As a result, despite 2 being the slightly better and newer eroge, I would strongly recommend playing 1, then 2.
Rather than provide a more detailed attempt to give a story outline, which is likely to lead to spoilers, I will instead focus on two elements, that for me, helped make both games some of my favourite eroges. The first is surprisingly, restraint. Although the content in both games is centred around extreme masochism, particularly in 2, the number of scenes that involve sexual depictions is relatively low. Both games do cross the line of realism at some point, particularly on the black events, although the extent to which they do is far less than most other Black Cyc games. For me, this made the scenes shocking, without being numbing and repetitive, and helped emphasise the horrifying, but fantastical setting. In addition, the masochism found in almost all of the ippu was not used solely for gratuitious purposes, but also had a justification within the setting that tied in with the overall story.
The second is presentation. Although both games have strong scenarios, have excellent characters, and are very well written, neither eroge would work without taking full advantage of the careful gradations that the loop mechanism provides. Certain scenes are omitted in earlier loops, and others may have slight changes to the visuals or dialogue that force a radically different evaluation of some situations. 2 takes this concept further than the original, by making heavy use of furigana, flashbacks and omitted words. This is done not only to increase the differences between the loops and to make the story slightly more obtuse, but also helps to highlight the themes of each eroge. The most obvious and frequently discussed of these is the contrast between the mansion and the outside world, although further into the eroge, others also come to the fore.
After working on Mugen Kairou 2, the writer and artist, along with another sub-writer released Cthulhu in 2010, which like both Mugen Kairous, had an interesting and original concept. However, Cthulhu's story suffered badly from being rushed and inconsistent. This could have easily happened to either Mugen Kairou game, but thankfully it didn't.

Briefly moving on to other elements, in every aspect the second game improves over the first. Although there are slightly fewer CGs in 2, the quality, accuracy of the lineart and detail is far higher. The BGM and songs in both are very strong, slightly better in 2, as is the game's engine, which is able to display furigana properly. Although the seiyuu in both games are generally not well known, they deliver strong, and in some cases outstanding performances in difficult roles.
Both Mugen Kairous are just about at the top of my list for eroges that I wouldn't recommend to an average person. However, for those that are open-minded, and wish to try two dark eroges that take full advantage of their setting to highlight external themes, both games are strongly recommended. Although my scores for both games are very high, and well above those that other reviewers have given them, I think those who are not put off by the extreme content will find that both titles provide much food for thought (particularly to those who enjoyed CROSS†CHANNEL).

Overall Score: Mugen Kairou 92%, Mugen Kairou 2 98%