Ninjas are masters of disguise.
Now we switch to the ninjas, and examine how we might be like them. One of the more reconizable (to be rather ironic) characteristics of ninjas is their ability to blend in. Not only are they quiet and stealthy (which we'll get to later), but they can fit into any situation and become who they need to be to accomplish their task. A ninja can appear as a farmer, a palace guard, or a simple merchant. They become whatever the job needs them to be, and use their skills in disguise to help them get closer to their target.
Similarly, when presenting the Gospel, we should seek to fit into our surroundings. By becoming like our audience, we can reach them in ways that standing out would never do. So maybe if we're at a con, we dress in costume and talk about comic books, pirates, and ninjas. If we're speaking to a group of medical professionals, we dress in a suit and use different language. Like Paul says, we should be all things to all people. We are commissioned by Christ to spread His word. Sometimes that means changing how we look and act, blending in like a ninja would.
Though I am free and belong to no man, I make myself a slave to everyone, to win as many as possible. To the Jews I became like a Jew, to win the Jews. To those under the law I became like one under the law (though I myself am not under the law), so as to win those under the law. To those not having the law I became like one not having the law (though I am not free from God's law but am under Christ's law), so as to win those not having the law. To the weak I became weak, to win the weak. I have become all things to all men so that by all possible means I might save some. I do all this for the sake of the gospel, that I may share in its blessings. (1 Corinthians 9:19-23)