@RainGnyu Unless you're killing things with another weapon you can't be doing anything wrong. Literally all you have to do is have the sword in your hand when things die in your current area. I think you may be overestimating how many kills you're getting per run of whatever you're doing though.
As I recommended earlier do 10 runs of Haru TA (which comes out to 1000 kills in about 30 minutes) and check the title counter. Repeat for as long as it takes. You can track what run you're on (and how many kills you've gotten) by typing what run number you're on in party chat.