Hey everyone! I'm going to speak about the differences is ranks.
Kage - The Kage(s) are the leaders of the village. Pretty much the strongest ninjas around. They are unbelievably fast and strong. Anbu and Sannin have the highest chances of winning or surviving against a Kage. Experienced Jounin also have a chance against the Kage(s). For Ninja under Jounin, it will be hard, but not impossible, to beat a Kage.
Sannin - The Sannin are the 3 strongest and smartest(battle-wise) ninja besides the Kage. Sannin-level ninjas are on par with Kage-level ninja, which means they are almost, if not equally, as strong as Kages.
Anbu - Anbu are fast ninja who have slightly surpassed Jounins in power but greatly in speed. They have alright chances in fighting Sannin and Kage level members. They are closer to Jounin than Sannin.
Jounin - Jounin are strong ninja who have almost the same stats as Anbu except that most Anbu are faster. Jounin have good chances in surviving against Kages and Sannins. They are on par with Anbu.
Sp. Jounin - Sp. Jounin are ninja who have surpassed Chuunins but have yet to reach the rank of Jounin. They are faster than the average Chuunin and also stronger.
Chuunin - Chuunin is the first rank you can earn. These ninja are just a tad bit faster than Genin but are a bit stronger.
Genin - The first rank available. Genin are very weak unless they use strategies to overcome the opponent. They are a bit slower than Chuunin but there isn't a very large difference. They don't have high chances in beating ninja above the rank of Sp. Jounin.
In order to get the rank of Chuunin, Sp. Jounin, and Jounin, you must have a ranking exam! There is a very slim chance of becoming a Anbu or Sannin during a ranking exam. Anbu and Sannin can also be chosen without a fight if a Kage watches over your progress and sees that you are ready.
Antagonists - Antagonists are ninja/beings that may attack our village in the future or just want to battle. These ninja are usually powerful but they don't have a set rank. They can be beaten by anyone and win against anyone.
Deceased - These are ninjas who have died. These ninja will have the same stats as when they died. (You will be able to use these characters in the near-future)