Isekai Nidome no Ossan, Dou Kangaetemo Koukousei Yuusha yori Tsuyoi

Riku Takayanagi is a boring 32-year-old businessman with nothing special about him. Or so it seems. In truth, he once saved another world as a hero. Now he's back in Japan, living a normal life... until one day, he's dragged into the mess with three high school students and summoned again—this time to a different world?! Suddenly thrust into the unknown, Riku steadies the panicked teen heroes, encourages them, and teaches them how to survive. The long-awaited opening to a second-chance another-world adventure—starring a caring, absurdly overpowered old man hero!

(Source: AlphaPolis)