Where does JJ Watt play?

I'm a 49ers fan with a quick question for you guys over here on r/Texans. I'm a bit of a NFL Draft junkie, and I've been trying to mock you guys some talent in the second round, but I just had a quick question on the way your guys defense works. I understand you guys mostly play in a 3-4 defense, but I also get that JJ Watt is regarded as an edge rusher. I've been confused on how JJ Watt fits into your defense. Does he play inside as like a 5T on rushing downs, and then moves outside as an edge rusher on passing downs? Does that mean edge rusher or iDL is a bigger need for you guys? If I'm just way off on the Texans scheme, then that's fine too, you guys can fill me in.