WARNING: The following contains spoilers for One-Punch Man Chapter 135, by ONE, Yusuke Murata, John Werry and James Gaubatz, now available in English from Viz Media.
The battle between Tatsumaki/Terrible Tornado and Psychos has escalated over the last several chapters of One-Punch Man, with neither party able to get a clear leg-up over the other. While Genos and Drive Knight have both stepped into assist, Tatsumaki needs a major boost to get her head back in the battle in One-Punch Man Chapter 135, which results in her thinking back to her relationship to Blast -- the number one ranked hero.
As Genos assists Tornado against Psychos, both the cyborg hero and her little sister -- Fubuki/Blizzard -- realize that Tatsumaki has actually fallen unconscious. From there, the manga launches into a flashback in which a young Tatsumaki is imprisoned at a research facility eighteen years prior. Soon, a synthetic beast breaks free and starts running amok in the facility. The researchers opt to abandon Tatsumaki -- the future number two hero -- because she's not strong enough. However, just when things look most dire, Blast appears, easily slaying the beast.
Blast reveals himself to Tatsumaki, explaining that he just does heroics for fun. He then asks Tatsumaki why she didn't use her psychic abilities, and she tries to lie and say she no longer has access to them. Blast calls her out, noting Tatsumaki actually believes the research facility might let her go if she doesn't use her powers. Tatsumaki then starts to get upset and cries, saying no one cares about her outside the facility. The future Tornado reveals that her parents actually sold her to the research facility, which is why she's stuck there.
However, in response, Blast tells Tatsumaki that Fubuki needs her, and that Tornado should protect her little sister. Then, he tells Tornado that she shouldn't expect someone else to save her in the future. Back in the present, Tornado wakes up after hearing her sister's voice and moves to join Drive Knight and Genos' attack on Psychos.
Just why Blast doesn't involve himself in the various world-threatening events that have plagued the One-Punch Man Universe isn't totally clear, but there may actually be a hint in Chapter 135. Like Saitama, Blast describes himself as someone who does heroics for fun. While this is far from confirmation of the fan theory that Blast and Saitama are the same person, this does indicate that he doesn't feel the need to be a hero out of any particular sense of morality. As such, Blast has very likely chosen not to intervene in the manga so far because he doesn't really care.
Although Blast has remained mysterious since One-Punch Man launched, the manga is finally starting to reveal more about him, and that could end up leading to some major revelations at some point down the line. However, One-Punch Man is making clear that Blast's past and how intertwines with those of the manga's other heroes matters just as much as his identity. In the case of Tatsumaki, Blast was an important figure, as he helped inspire the future number two hero to fight harder and train.
One-Punch Man Chapter 136 does not have a release date at this time.