Information on Uatu the Watcher: http://en.wikipedia.org/wiki/Uatu
So here we have two foes of completely different universes pitted against each other. They have much in common - both are committed to non-violence, and both are content with their roles as teachers and heralds... but in one special way, they differ.
Itoshiki is "the ultimate pessimist", always in despair (as per his name) and looking for a means to commit suicide.
Uatu is an immortal being with an unbiased opinion of everything, life and death included. The only way he can die is if he himself wills it.
...so who wins? Will Itoshiki drive Uatu into despair, or will Uatu help Itoshiki see the light in the darkness of the world?