>>75437917tl;dr: caffeine makes you feel less drunk than you really are making it more likely keep drinking past your limit and end up completely shitfaced, which is why doctors advice against it, specially if you are a teen who doesn't know their limits yet
Will it kill you? Most likely not unless you drink so much you give yourself alcohol poisoning or try driving since you don't feel drunk and end up crashing because your reaction time is still fucked up
Is it something you should be telling people to do in a sponsored stream for an energy drink? Hell no, which is why the sponsor felt obligated to do a "we checked with out lab guys the caffeine content in our drink was deemed safe, and the proposed mix is comparable to other caffeinated cocktails, drink responsibly, oh yeah this was Niji's management idea, btw"