In Another World with My Smartphone, Vol. 3 (Manga)

Nefarious schemers have attempted to poison the king of Belfast and frame an innocent victim. Touya knows the truth, however, thanks to the abilities he gained upon being transported to this new world. But while his goal is to corner the culprit, Touya has something else to worry about--his helpfulness has attracted the attention of the king's only daughter! Princess Yumina wants Touya's hand in marriage, and she won't take no for an answer...