Finding Manga

Im looking for this one fantasy Manga. Its about a guy waking up in a random forest, but not in his body. hes nwo something like a wraith/ghost and quickly learns, that he can suck out the "life" of things. Through that he also learns of magic and then later gets really good at it because he uses laws of science. He then later takes on a student (girl) and teaches her magic. In their World People that are good at Magic get titled as something equal to a "hero" i think they call them paladins or so. She then gets stronger and some random guy from her unit likes her and "wants" her. Our MC notices it and gets mad when the bad guy nearly does something to his student (the girl). He then kill the bad guy brutally . I dont know any more but I really wanna find it and read it again. PLS Help