I played the Neptunia Re;Birth games, and those can be a pain in the ass regarding collectables.
Each game has at least a bad ending and a good ending. The first game wasn't too bad, just balance out four different point values before fighting the final boss. The second game is where things get complicated. There is a different ending depending on your relationship values with each of the optional characters, a different ending depending on which of the four point values (returning from the first game) is greatest or if they're all balanced out, a different ending depending on if you found a couple hidden items, and a different ending depending on if you found some hidden information for your characters to know regarding said hidden items.
The point value-dependent endings rely on the same requirements as the first game, just pick some compatible side-quests at any point and start manipulating numbers. The secret characters are a bit more of a pain, since you have to drastically alter the point values to get each one, so you dump points into one of the four countries to get one set of characters, then start slowly transferring points to another country to get its set of characters. Slower, but not too bad. The real pain is when you have to manipulate relationship values and the hidden information for your characters to discover.
The hidden information is only available during a certain chapter of the game. If you don't stop between every level and check the overworld for informants, you'll probably miss one of the three bits of info and you'll be drug into the worst ending. If you do manage to catch all three before they disappear, you get one of the best endings. Note that I said "During" a certain chapter, and not "by" a certain chapter. The informants only appear partway into the chapter, and they permanently vanish after the chapter ends, with absolutely no warning to the player that they're present or even important.
The relationship values are irritating for another reason. You need to balance out relationship values between all of the different characters in different ways, with certain characters needing to have the highest relationship value in order to get their respective endings. The game is nice enough to give you stackable New Game Plus playthroughs, so you can repeatedly zip through the game with ever-increasing stats and equipment. However, relationship values also carry over, so if you got high relationship values with certain characters, it's going to be really hard to get certain endings that require other characters to have higher scores. Worst-case scenario, you're going to need to start another from-scratch playthrough to reset those scores and try for the remaining endings.
Of course, if you were smart enough to realize that this would eventually happen, and you have yourself a base save file to split each subsequent playthrough from and give yourself a more convenient restart point, you didn't have as much trouble. Of course, how many games nearly require precise save-file manipulation across multiple slots in order to get everything?