its tough for new ninjas to rise up the ranks and to compete with the more seasoned ninjas, i propose a system where a higher up ninja could take a new player under their wing and help them grow, a character who has reached a certain level, we can say something like at least level 30, and you must be 5 or 10 levels above a player to accept them as an apprentice.
an apprenticed player would gain 25% exp from all sources. while the sensei would be given 10% extra on coin rewards for each apprentice, and when looking at the profile of a ninja you could see any ninja that that player is either apprenticed to or apprenticing. and a player could only be either an apprentice or a master, a player who has an apprentice could not be another player apprentice themselves, and a player who is an apprentice would be until to take apprentices.
there would be a limit of how many apprentices a ninja can have, starting at 1 at level 30, increasing by 1 for each consecutive 10 levels. a ninja could also buy apprentice slots in the store for ingots, with a maximum of 5 or so. An apprentice could only have 1 master at a time however.
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there was a similar system in "unlimited ninja" where strong players could enslave other players by battleing them, the master would gain coins while the slave would lose coins, there was an option to give gifts to the master, to fight the master for freedom, and for the master to "pet" the slaves which would give them some exp. you could also steal slaves from other players if you could beat them in battle. a title would be given to each player, either master, slave, or free. a free ninja could enslave other ninjas by battleing them, a master could not be enslaved until all their slaves were taken, and a slave could be stolen by other masters.