This Is the Wizard's Secret Weapon, Vol. 2 (light novel)

A blast from the past comes crashing into the present! Thanks to his unique skill set, Rix has been allowed to stay at the academy in spite of his magic deficiency. But even with Shino’s constant guidance, his grades are catastrophically bad, and the threat of expulsion once again looms large. As if things couldn’t get any worse, Tran, his sister-in-arms from his mercenary days, shows up intending to drag Rix back to the battlefield. And when she throws around her dragon powers on school grounds, Rix’s newest problem is…immediate expulsion! In a last-ditch effort to not get kicked out, he tries forming a contract to make Tran his summoned creature—with shocking results!