As fans may remember, when My Hero Academia was inching towards its conclusion, mangaka Kohei Horikoshi brought Katsuki Bakugo "back from the dead." While that was a pleasant development, many fans questioned the creator's lack of commitment to killing off his characters.
Nevertheless, as one could observe, at least in Bakugo's case, the creator justified his survival at the expense of Pro Hero Edgeshot turning tiny. That wasn't the case for Gran Torino. Shigaraki Tomura dealt a heavy blow to him in the Paranormal Liberation War Arc. However, the series revealed that he survived the injury without any justification.
Disclaimer: This article may contain spoilers from the My Hero Academia manga.
Kohei Horikoshi never explained Gran Torino's survival in My Hero Academia

As fans must remember, Gran Torino faced Shigaraki Tomura during the Paranormal Liberation War Arc. While fighting him, the villain grabbed his left leg and crushed it before shoving him onto the ground. While other heroes tried to reach them, Tomura continued his onslaught by brutally smashing his arm through Gran Torino's chest.
Under normal circumstances, any hero would have perished after having dealt such a blow. However, Gran Torino managed to survive his injury, after which he was treated by the paramedics and transported to a hospital. While he was in a very weakened state due to his injuries and remained bedridden till the end of the series, Kohei Horikoshi never justified how he survived the ordeal.

As any manga reader would know, shonen manga has a trope where the death of a protagonist's mentor allows them to reach new heights. However, as evident from how All Might and Gran Torino survived in the series, Kohei Horikoshi may have wanted to break free from the trope.
However, unlike most anime MCs, Deku did not have one or two mentors, but plenty of them, such as All Might, Eraser Head, Gran Torino, Sir Nighteye, and Endeavor. Out of them, the only one who passed away was Sir Nighteye. While that development impacted Izuku Midoriya, it was in poor taste as the Pro Hero was killed off in the same arc he was introduced.

This development effectively meant that Kohei Horikoshi only introduced Sir Nighteye so that he could spare his existing characters and sacrifice him for Deku to experience the "mentor's death" trope. Instead, the manga creator could have used Gran Torino for the same purpose.
The character had already mentored three One For All users and had plenty of achievements under his belt to die with no real regrets. Not only did he keep his promise to Nana Shimura by training All Might, but did a remarkable job with Deku after coming out of retirement. Therefore, considering that he was already an old character and had his torso destroyed by Shigaraki, it would have made more sense for him to pass away.

Such a development would have not only impacted Izuku Midoriya but also Toshinori Yagi, allowing them to surpass their limits in the final battle. Fans must also remember that, before the Final War Arc, Gran Torino handed his cape to Deku. The same development would have felt more impactful had the protagonist inherited the same from his mentor after his death.
Regardless, the Pro Hero was shown to have survived against all odds. In fact, the manga also showed Toshinori Yagi visiting him months after the end of the Final War.
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