When the guy's more beautiful than the girl and the girl's more handsome than the guy...
Still tho, it is the best possible ship that won't spiral into an outright disaster atm. Every other possible pairing will most definitely degenerate into shitstorms of varying magnitudes.
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"When there is evil in this world that justice cannot defeat, would you taint your hands with evil to defeat evil? Or would you remain steadfast and righteous even if it means surrendering to evil?" - Lelouch vi Britannia as Zero.