Brazilian Jiu-Jitsu (BJJ) and Japanese Jiu-Jitsu (JJJ) have distinct characteristics and origins, despite both stemming from the traditional Japanese martial arts. Here's a comprehensive comparison based on the information gathered from various sources:

1. Origins and Evolution

• Japanese Jiu-Jitsu: Originated in Japan as a method of close combat for defeating an armed and armoured opponent, focusing on using minimal force. It includes a wide range of techniques, such as strikes, joint locks, and weapon use​.
• Brazilian Jiu-Jitsu: Evolved from Japanese Jiu-Jitsu and Judo. It was developed in Brazil by the Gracie family after Mitsuyo Maeda, a student of Judo founder Jigoro Kano, taught Judo to Carlos Gracie. The art was adapted to focus on ground fighting and grappling, making it suitable for smaller practitioners to defeat larger opponents​​.

2. Focus and Techniques

• BJJ: Emphasizes ground fighting and submission grappling, using chokes, strangles, and joint locks. It's designed to control and submit the opponent on the ground, allowing smaller individuals to overcome larger ones​​.
• JJJ: Encompasses a broader range of techniques, including throws, joint manipulation, and even some striking. It's more varied and can include the use of weapons and other self-defence tactics​​.

3. Training and Competitions

• BJJ: Training typically involves 'rolling' (sparring), and competitions are a major part of its culture. These competitions are usually organized in a bracket-style tournament with weight classes​​.
• JJJ: Training can be more varied, including kata (pre-arranged forms) and live sparring. Competitions exist but are less prevalent and vary in format and rules​​.

4. Rules and Regulations

• BJJ: Has more strict rules in competitions, prohibiting certain techniques like striking, neck cranks, and some leg locks​.
• JJJ: Offers a wider range of techniques in training and competition, including some that are not allowed in BJJ​.

5. Belt Systems and Progression

• BJJ: Uses a belt system that typically includes White, Blue, Purple, Brown, Black, and higher degrees of black belts. Progression is based on technical knowledge, sparring proficiency, and time spent training​​.
• JJJ: Belt systems can vary, but generally include White, Yellow, Orange, Green, Blue, Purple, Brown, and Black belts. Some schools may start beginners at a red belt​​.

6. Cultural and Philosophical Differences

• BJJ: Reflects the Brazilian culture of being less formal and traditional, which is evident in its training and communication style​.
• JJJ: Maintains a strong sense of tradition and discipline, reflecting its roots in Japanese martial arts culture​.

In summary, while both BJJ and JJJ share a common lineage, they have evolved in different ways. BJJ focuses more on ground fighting and sportive aspects, whereas JJJ encompasses a broader range of techniques suitable for self-defence and maintains a more traditional approach. The choice between them depends on personal preference and goals, whether it's for competition, self-defence, or embracing a specific martial arts culture.