Towards the end of Season 1 of Demon Slayer (Kimetsu no Yaiba), we come to know about Total Concentration Breathing. It was introduced as a technique which every Hashiras and expert Demon Slayers uses. Basically, it gives a user flexibility, power and ability to control the body properly and efficiently, which makes a whole lot of difference to Demon Slayers.

What is Total Concentration Breathing?

It is a high level breathing method where a user breathes in the oxygen controllably to raise their physical and mental power to their utmost limits. This provides the user upgraded physical and mental capacities, as superhuman qualities (for example strength, speed, endurance, solidness and readiness), quicker points of view, expanding focus and thoughts process. At a further developed level, Total Concentration is likewise equipped for stopping injuries from getting more serious and stopping the flow of toxin in the circulatory system.

Tanjiro uses Recovery Breathing to focus and steady his breath which allows him to recover from fatigue and stiff muscles that prevented his body from moving due to after effects of using Hinokami Kagura techniques twice in a row.

Total Concentration: Constant is a state of maintaining Total Concentration breathing during the morning, noon, and night, and even while asleep. Every Hashiras and expert Demon Slayers do this which creates an immense difference in strength, speed, and stamina between someone who can maintain Total Concentration Breathing at all times and someone who cannot.

As seen in the anime and mange, a special thick hard gourd is used for training to use and maintain Total Concentration Breathing properly. As you make progress and improve, you can blow hard to make the gourd break apart. After being able to break one size of gourd, it continues to another bigger gourd than the current size.

Is it real?

Yes, it's real. Though not to the extend of Demon Slayer, but yes. You may have seen people doing superhuman feats like staying in ice for long time like Wim Hof. Staying in cold is really dangerous and could lead to hypothermia, causing even death. How does it relate to breathing? Well, people performing these stunts have mentioned that proper breathing technique is a important factor along with training.

There are lots of breathing techniques focused on different outcomes. Reverse Breathing, Breathing Rhythm, Kiai, Kokyu Nage, Kokyu Hu, Buddhist Vase Breathing, Golden Elixir Breathing, White Tiger Breath are some breathing techniques used in martial arts. Box Breathing, Belly Breathing, 4-7-8 Breathing are some breathing techniques common to control stress and anxiety.