The lord of the Dragon Domain would dare frame an apprentice Grim Reaper signed by hell?
Besides... Miss Venus seems to be clever as ice and snow, not the type to be easily duped.
Also, how did the Evil Dragon know that the lord of the Dragon Domain would trick... oh, I remember now, the Evil Dragon once stayed in the Dragon Domain, he even served as a lord there...
During his tenure as a lord, he must have interacted with the other lords of the Dragon Domain, it's just unclear whether he ever beat up those lords or not.
The Evil Dragon wouldn't start trouble on his own, but if those lords of the Dragon Domain came looking for trouble with him, the Evil Dragon might be quite pleased, he likes having justice on his side.
Standing on the high ground of justice, he silences those who provoke him.
The Evil Dragon is a morally upright Black Dragon.
But the morals of a Black Dragon... fluctuate wildly... sometimes there, sometimes not...
His actions are very hard to predict.