we all know that
1st tomoe:your very own happpily ever after ending of a near-death experiance
2nd tomoe:i would say abandoning your village and betraying your friends
3rd tomoe:fight your best friend in a death match
pre-mangekyo:kill your brother or sister cousin clan member etc.
mangekyo:kill a kage or sannin(but in my cases all in my clan im mentally deranged i could attack at any moment...like now o.0)