Any DMC game from DMC2 and on. DMC4 and DmC in particular. DMC2s troubled development which started as a different game without Kamiya knowing and included the original director quitting, Itsuno almost leaving after 2 was such a massive disappointment and the extreme turnaround with DMC3 and its rapid development, followed by 3SE and DMC4 in rapid succession, then DMC4s extremely rocky development that probably mirrors that of other early HD game from other pubs like FFXIII and MGS4, then Capcom JP asking Capcom USA to take over for the next game, leading into DmC, then the series' fate post-DmC. Might be impossible because it's a mostly Japanese series, but anything you could find out that isn't public knowledge would be amazing.
PS1 era Squaresoft would be interesting as well.