if you really wanna do a superhero flick, from the top of my head I can give you a couple of random ideas and hope it helps.
i'll give you two classic and cliche ideas and 2 fairly original ones.
-boy in the delta discovers he can save the "bad guys" from shutting down the river and killing the animal life, he does so by getting powers from somewhere, maybe aqua powers so you can do some rad water shots..
-a man decides he will raise a colony of undead to raise hell on earth and this boy is the only one who knows about it. he discovers amazing powers that grant him imunity against the undead and over time defeats an entire army
now 2 ideas i'd maybe try doing from the top of my head:
-a teenager gets so lost in comics and movies that he thinks he is a super hero, he falls deeper and deeper into his imaginary world, almost to the point of getting killed, he is helped by his female friend- in the end he learns that the real world is too sad for him to handle and decides to live in his imaginary life, therefore going deep into a kind of mental illness.
-maybe an idea of a guy who is nothing special and decides he will help others with his human powers, he makes a semi-costume and helps everyone with his human capabilities. kind of a short film showing that every human being can be a super hero if they wanted to.