Obviously, it's Ruukuto.
The mystery of shadows refers to the mysterious way that she is both acquired, then lost.
the epilogue of the sun powered by nuclear fusion, that which is the power that will lead stars to their inevitable demise.
The drive of a madman the robot maid was created (or gifted, not too sure) to Reimu by Yumemi Okazaki, who is regarded by her peers as being mad or insane.
the results were none and this is where I stop giving a shit about whether or not I'm right or not.