Inkyogurashi no Ossan, Joou Heika no Tsurugi to Naru

Watt Sears has traded his glory days as a Mechsteel knight for a humble life as train station employee with a knack for showing new pilots the ropes. Problem is, the city's baron—his boss—would love nothing more than to see Watt reclaim his old mantle as a Steelrider who hunts monsters and defends the city. Now nearing forty, the once-legendary pilot would much rather support the new generation than stand in the spotlight himself. Peace and quiet were the last things waiting for Watt, however, as his storied past literally comes to find him. When Anna, his long-lost daughter from a bygone romance, appears before him to ask for his help in a brewing royal power struggle, Watt vows to protect her. But as assailants descend on the city from all sides, keeping his promise proves to be no simple task. With turmoil rattling the kingdom, can this old knight survive his new post and keep his daughter safe?

(Source: J-Novel Club)