The Misfit of Demon King Academy X That Time I Got Reincarnated As A Slime

Why did Anos suddenly decide to sacrifice his life to end the war 2,000 years ago?
As the reincarnation of the Demon King of Tyranny, this Voldigoad possessed nigh-insurmountable power that many attempted to challenge to no avail. Despite being a hybrid by birth, Anos excelled at school and amassed a following of hybrid students who realized he was the original demon king from millennia ago.
This fan fiction is with anos and rimuru.
Rimuru initially appears as a blue-bodied Slime, but upon becoming a Demon Slime, his body turns silver with streaks of gold.As a slime, since his body is androgynous, anything he mimics takes on an androgynous form of the respective creatures, while still bearing huge resemblances to the individual creatures as well.His mass also grew over time, allowing him to accommodate larger mimicry forms without using extra magic to compensate for the additional mass. Towards the beginning of the story, he only has enough mass to appear as a human child, but each time he consumes a foe powerful in relation to his current strength, his size in human form shows a notable increase.