Akatsuki no Goei is something of an oddball if you ignore the existence of Grisaia, but they share some major traits. Both have a relatively 'peaceful' (if dramatic) first game that involves romantic paths that are mostly irrelevant to the third game. Both have a psychologically-scarred, killer protagonist with a criminal past. Both have a quirky sense of humor that is mostly generated by the protagonist's abnormal actions... I could go on, but I'll move on to my point.
The most blatantly obvious similarity is that both series have three games, the first, the fandisc, then the third as a conclusion. In both cases, the conclusion is more serious, but that is where the similarities end. Whereas Grisaia's third game went down the kinetic novel path, giving you only one ending to see, Akagoei's third game, Tsumibukaki Shuumatsuron actually has three main routes with over fifteen endings, each with a different heroine.
Now, I'm going to hit the titular reason why I wrote this post. Akagoei can be seen one of two ways, based on knowledge gained from playing Reminiscence. You can either see the fandisc as irrelevant save for the long experience of Kaito's past seen in Anzu's route, giving you the background knowledge to give flavor to the third game.... or you can see the FD's endings as an alternative to the ones in Tsumibukaki Shuumatsuron, a conclusion that a lot of the fans of the SOL and comedy elements of the series picked.
This is actually very typical of Kinugasa Shougo. Kinugasa, from all accounts, hates canon endings. He doesn't like to produce firm conclusions, and he always wants to leave the reader guessing on one level or another. I'm about 90% sure Kinugasa created Tigre and made Reminiscence solely to make people confused, because it draws elements from all three games into the background, while not telling you what actually happened at all. A few of those elements include: Akemi's path events in 3, Tae after-story from the FD, Reika path events from 1 and 3, and any number of other things. It is also pretty clear, probably intentionally so, that a lot of the characters from Akagoei left descendants to appear in Reminiscence, though you can only guess who is who by appearance and their roles in the underground society.
In other words, feel free to draw your own conclusions when it comes to this series... that's about half the fun.