I met an instructor,

he said nice to meet you I am your instructor

then

 he suddenly asked me do you know how to kill people?

 I was surprised by the question he asked.

 I remain silent

Then

 he said I will take that as a no. I will teach you how to kill

 then

 he taught me everything he even taught me alchemy and magic.

 Then I became a mere test subject for them I went to the battle ground and started killing and to hide my identity I wore a cape and the mask that minato gave me.