I'd probably allow a character with that as their schtick. If they can find a way to do it without me needing to homebrew anything that's great, but I'm still going to try my hand at it anyway.

Personally, I think it's interesting. It requires melee combat so it shouldn't necessarily be overpowered, and there are lots of roleplaying oppotunities if it can't be turned off. Unfortunately not many systems have support for such a character (the system I'm making can't really handle one as a PC without significant homebrew or inherent imbalance, for example, you either need to make something new for everyone or accept that character X is slightly to largely more powerful than the rest of the party).