Kid Gilgamesh. While he may not be as powerful as his adult form, child Gilgamesh is, on the whole, a far more pleasant person to be around. Also he stole Illya's heart (again) by calling her Onee-chan.

(Illya has an onee-chan fetish?)

and Caster Gilgamesh. Coming from later in Gilgamesh's life. While he may still be a tad bit arrogant, on the whole, he's much wiser man than his younger Archer self

Plus, unlike most traditional Casters, he at least brings a weapon to bear in the event he cannot use his Magic without risk of injury.

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no matter what the age, Gil always finds his way to Illya's heart.

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Hah