The Zen clan's history starts with a legend of the first two Zen, sons of the Great Zen, Muu, Muramasa and Musamune. After the fall of the former smiths of the Seireitei, the Zen Clan a notable family of smiths were called from the harshest district on the East side of the Rukongai. A legend tells of a test where Muramasa challenged his brother, Masamune, to see who could make a finer sword and who would lead the clan in their new duties when they entered the Seireitei. They both worked tirelessly and eventually, when both swords were finished, they decided to test the results. The contest was for each to suspend the blades in a small creek at the edge of the Rukongai with the cutting edge facing the current. Muramasa's sword, the Juuchi Yosamu (十千夜寒, "10,000 Cold Nights") cut everything that passed its way; fish, leaves floating down the river, the very air which blew on it. Highly impressed with his brother's work, Masamune lowered his sword, the Yawarakai-Te (柔らかい手, "Tender Hands"), into the current and waited patiently. Only leaves were cut. However, the fish swam right up to it, and the air hissed as it gently blew by the blade. After a while, Muramasa began to scoff at his brother for his apparent lack of skill in the making of his sword. Smiling to himself, Masamune pulled up his sword, dried it, and sheathed it. All the while, Muramasa was heckling him for his sword's inability to cut anything. Their father, who had been watching the whole ordeal, walked over and bowed low to the two sword masters which he had begotten. He then began to explain what he had seen.

"The first of the swords was by all accounts a fine sword, however it is a blood thirsty, evil blade, as it does not discriminate as to who or what it will cut. It may just as well be cutting down butterflies as severing heads. The second was by far the finer of the two, as it does not needlessly cut that which is innocent and undeserving. To make a fine weapon you must have a meditative, peaceful mind, taught Muu as he honored Masamune as his heir and made Muramasa his second, creating the main and branch family of the clan."

The Zen Clan members all harbor black hair and crimson eyes. Their teaches are to keep a meditative state throughout life so that they can achieve Asauchi as pure as "Yawarakai-Te" which was the holy sword which Masamune created, so that they can be bonded perfectly with their Shinigami partners.. It and Juuchi Yosamu still sit within the throne room of the Zen Clan compound. Being that this meditative state resists violence, the Zen Clan have kept its members out of the Gotei 13 since they've entered the Seireitei. Mugen Zen the last heir was the first to enter the Gotei, taking the ancestral sword which Muu "The Great" Zen created, Fūrinkazan, now Mugen's Zanpakutō. He exiled from his clan because of this and replaced with his younger brother. But he has been able to retain his meditative state even within the heat of battle and never lost his Asauchi creating abilities.

Main Branch Line:

• Muu "The Great" Zen
  
  
• Masamune "The First" Zen
  
  
• Musashi "The Second" Zen
  
  
• Hōzoin "The Third" Zen
  
  
• Mugen "The Departed" Zen
  
  
• Mugai "The Fourth" Zen
  

Branch Family Line:

• Muramasa Zen
  
  
• Kanemitsu Zen
  
  
• Kinju Zen
  
  
• Kuneshigi Zen
  
  
• Kunitsugu Zen