What is the rush to learn another style or something new? By reaching your first dan you have just opened the door to the style your in. Too many times students get a false sense of confidence by getting their black belt. Stick with your style for a while after you get your first dan, you might be surprised at what you will start to learn. If there is nothing left to accomplish then move on.

For weapons, Kendo is alright. Other options include Okinawan Kobudo (traditional Okinawan weapons such as sai, bo, and kama), Kali/Escrima/Arnis (Filipino stick-fighting systems), and any system of Kung Fu that includes weapons training, which is actually quite a few of them.

black belt means you have the basics down, and still have a long way to go to get to master, if you want weapons try arnies

you should stick to the karate until first dan then crosstrain in another style.i would choose muay thai which will help you improve your fitness and stamina,which will help you with your second dan grading.it will also help improve your knees and elbows.you could also crosstrain in a weapons style or ground/grappling style later on.you should keep karate as a base and cross train in other styles.

Talk with your instructor about supplementing your training. Most people believe that you should so a “soft style” to compliment a “hard style.” Others like to do variations of what they’re doing or something totally new.

After I got my black belt, my sensei started teaching all of the black belts Iaido. Now that is something else. Some day, I’d like to go completely off the reservation and learn the rope dart.

Getting a Black Belt doesn’t mean that you have mastered the art . It actually means you have just begun. So be careful with the over confidence thing. If you learn everything there is to know about your art by reaching black belt — then your art is shallow.

Brazilian Ju Jitsu.
So then you can choke motherfuckers out.

A martial art that incorporates grappling. For example -

Brazilian Jiu jistu
Judo
Sambo
Wrestling
Jiu jitsu
Aikido
Hapkido
Sumo

ground fighting like sambo , jujutsu, or brazi-lion-gee-ooo-jeet-sooo

cali