Spoiler!
A long time ago, The g** of underworld Hades fell inlove with a certain Demi-goddess named Persophone.
(Daughter of the goddess demeter and mortal man)
As she only possess 1/8th of a gods lifespan.
He then plead the king of the gods, Zeus, His own brother to give him a drop of "sacrament of Immortality" to make his lover into a full immortal.
Zeus agreed and gave his blessing towards the two lovers Although, He warned Hades
"If the daughter of demeter gave birth to your first child, Never make them step out of the Underworld or if they so,
They will become a mortal being like they were supposed to be and will forget his true identity and love ones"
The two couple agreed to the price of Sacriment, They both thanked Zeus and head to the underworld.
A Hundred years later, The Wife have finally gave birth to a twin. One girl that was named Melinoe and One boy named as Zagreus.
Confused on whose the eldest, The Hades assumed the youngest (Melinoe) as the older one.
Time passed and he became more protective and sensitive at the "younger" sisterand While Neglecting his true eldest child, Zagreus.
in a pathetic excuse of being busy at the work of underworld
Neverless, He is still Monitored by his father's underling who is also his childhood friend, The g** of Death, Thanatos Accompanying him Sometimes
The eldest became rebellious, Hot-headed and A prankster one, Causing trouble for everybody.