When the diety died without telling his people who next two rule, Adlaw and Mayani has been claiming the throne. But, they have different consequences. Adlaw wants a solo reign while Mayari wants a joint reign. This lead to a fight and out of anger Mayari hit one eye of Adlaw causing it to fall off. Out of Mayari's conscience they made a deal. Adlaw will have the kingfom half of the day while the remaining time will fall to the hands of Mayari. 

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This is also the reason why the Moon has a dim light compare to the Sun.