Compersion - The feeling of joy one has experiencing another's joy, such as in witnessing a toddler's joy and feeling joy in response. The feeling of joy associated with seeing a loved one love another; contrasted with jealousy.
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They loved, truly and simply. The world could be cruel, and uncaring, and harsher than the Arctic; it never bothered them. One house, three people, three hearts, and enough caring and understand for ten. It was how they worked. Do the headcount:
Allen Walker; small, a corporeal ghost, with all the delicate beauty of a willow maid (Allen - harmony, stone, noble, fair)
Kanda Yuu; tall, brash, but fitting of his name all the same (Yuu - excellence, superiority, gentleness, brave)
Alma Karma; an interweave of that came with opposition (Alma - kind, fostering, nourishing, good, loving)
And so, they loved. Simple and sweet and true.
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A series of Yulmallen fics and one-shots