Read Warlock of the Magus World Light Novel :
When a futuristic scientist is transported into the body of a young man in a fantasy world, his curiosity and desire for power push him to pursue magic. In a world without mercy, Leylin has no qualms about doing anything if it means benefits. He is cold, ruthless and calculating, never forming attachments that could impede his ultimate goal…
Honor? Who needs that… Hmmm… that guy seems too powerful for me to take on now… I better keep a low profile for ooooow.
You want me to help you? What benefit can I get out of it? None? Bye.
Hmmm… that guy looks like he might cause me problems in the future. Better kill him now before he becomes a problem…