mayb its a different time of day? bcoz ppl r only around @ certin times

He only appears in the evening. Then go check it out. He's there

I go at night after twelve a.m. and he isnt there, the one selling the coke and the
million dollar pistol is there and the fake i.d. guy is there but the guy behind the house
selling the katana and the AK isnt showing up. i dont know if its because my karma or
what..

It must be a glitch... Or he may only appear at Certain times in a random day. try 10 pm
or 1 am

he appears every couple of days past midnight. the more you buy from him, the less often
he shows up. but he never just stops coming. you should check every day for about 2 weeks
for him and he'll show up.

hes only there at 2 a.m

go to the shop next to the base ment and work there keep getting promotions and you will
get a sword better than the one hes sellng you

What shop next to the basement

There's a store to the right of the apartment you live in. It has a big blue X on it. It
represents XGenStudio. Anyways, work there and raise your Charm and Intelligence, I
think. I forgot if that's right. Anyways, just work there and try getting promoted.
It'll tell you what stat(s) to raise. Once you become the highest rank there, you win the
Masamune, a sweet sword.

Hope I helped!