If you look at karate as self-defense and you look beyond the techniques as just being blocks, punches and kicks, then you can clearly see that karate also has many applications that are also found in other martial arts. Below video shows a seminar where karate and aikido go hand in hand.
At the 1 min mark you will see the following applications:
Karate —> Age Uke - Kizame Mae-Geri - Giyaku Tzuki
to Aikido —> Ikkyo
And at 2 min 35
Karate —> Shito