Every fighting game with an AI that can pull off moves faster than me on a penny, and the Soul Calibur series shows no remorse.
Soul Calibur II: You cannot have a perfect record on all your characters that you used (you just cannot, seriously), and you have to beat Weapon Master twice. The first go is reaching the other side of the map (east) under leveled and with fewer weapons, and the second go is to finish the extra missions with even harder stage conditions. After that, you then have to unlock all of the menu options, stages, and characters. Depending on which version you have, you have a different bonus character from another game that you can use.
Soul Calibur III: In this one, you have a lot more to do than the last one, but you get to have a ton of fun for a long while. You get to experience every single character's story even more by playing as each of them, including some new characters. However, if you want to beat up Night Terror and not Abyss, you have to follow a set path without losing once or ringing out, and man up your skills against perfect-play AI in certain bonus stages with conditions, which you can't easily beat 95% of the time. Especially in the Labyrinth that is a one-way, you lose you're out of here route. If somehow you're extremely lucky, Night Terror rips you up a complete new dimension of what it means to be a player in a fighting game.
Oh, it even gets even more interesting with the RNG factor for AI skill in World Competition, where you have to sit through three to four hours of no saving, no choice of choosing a name, no SE, and not even your created characters for 12 rounds, 7 matches each. In Tour mode, you cannot ever lose a single match the whole way, and you have 3 chances to beat each random opponent. In League mode, while you are able to lose matches, you still have to reach 1st not only by beating more matches than your opposition seed, but you also have a better battle count, because there will be some better opponents being able to climb up the rankings easily. In the later rounds and from some opponents, the AI ramps up to a point you just have to give up and retry or rage quit. You get lots of cool stuff along the way and plenty of in-game gold to spend with if you win all 12 rounds.
With the new Chronicles of the Sword, there is no way you can perfect your runs, and speed running with care is a necessity to win some tougher missions. Getting the fabled weaponry with four effects is a big deal, it can cost roughly 50,000 to 100,000 and acquiring disciplines early on can be a chore. Soul Arena is another layer of adding up the difficulty, if you cannot handle the clichéd AI playstyle, then you are not worthy of getting the gold on all of the 12 missions.
Finally yet importantly is the Tutorial section where you have to master every single character's moves the game tells you to do in order to get the purple-white livery Ancient weapons, though they look cool as a skin, it’s just aesthetic in nature.
Soul Calibur V: Things have gotten a lot darker in this new game, and sadly, there isn't much you can do unless you're planning to go online and earn some cool achievements, rewards, and better ranks. With the Malfested plague becoming more prevalent across the world, yet due to time constraints as far as every Soul Calibur fan knows, the Story Mode returns yet again with Patroklos, a hero from Greece who is trying to return home but faces numerous obstacles along the way. You also get to control her sister, Pyrrha, and you get to have two forms with both of them as separate characters, along with Z.W.E.I. There aren't that many characters and stages in this era of Soul Calibur, so your options there are limited. The AI at first in the story doesn't get the better of you until you're about nearly the end where the difficulty spikes to a new level, but can be beatable. Don't you even dare try Legendary Souls mode, only a godlike player with extremely fast button mashing powers can defeat them, and even then, the AI can mash buttons and pull off difficult moves right away the instant a match starts. In this game since IV, you can no longer guard as much as you used to before, because now you have a defense meter, and you can't GI or GB the enemy until you have sufficient energy to do so, encouraging you to play in a more aggressive, reckless manner to beat your opponents. They make the inputs for guard impacting, guard breaking, and Critical Edges a bit harder to minimize abuse of these moves, but the AI can pull those off easily if they have the required energy. Lastly, if you are one battle away from victory, expect your opponent to power up one full Critical Edge bar for massive damage on you to make a comeback. You won't get gold in this, but you level up instead to unlock stuff, even if you lose battles.
[spoiler]
Oh, and did I forget to mention that in SCV, given the new clothing system, you have to prepare to resist the temptation to feel ashamed and look away if your character's clothing or your opponent's gets too damaged after a powerful enough blow upon defeat that it makes a breaking snap sound. This also applies in Practice Mode during customization when you're testing out your new characters against Edge Master as the test A.I.
[/spoiler]