Hazure Skill: The Guild Member with a Worthless Skill Is Actually a Legendary Assassin, Vol. 4 (manga)

When Roland receives a letter from the king personally requesting his assistance, he has little choice but to respond. Upon his arrival, he finds the king arranging a marriage between his daughter and a prince from the Holy Land of Rubens, a neighboring country whose influence spreads nearly as far as the Felind Kingdom's. With an alliance between the two nations being the ultimate goal, it's up to Roland to take command of the king's forces to ensure that no ill fate befalls them on their journey, and his mettle will be tested before long...