Calibur was revealed as not Kento's dad, but the original Saber, who saved Touma as a boy. The girl who got sucked into the book was Luna, who was another close friend to Touma & Kento, but one who apparently appeared just as mysteriously as she disappeared & she was sucked into a dimension housing what is left of the original book that the Wonderride Books spawned from, which now only contains the Table of Contents. Now that Touma knows this, he is in a lot of pain over not being able to protect people close to him-- moreso given what happened next.
After a lot of back & forth on the matter, Kento did eventually die at the hands of Calibur, though I don't know if it's permanent, & Calibur himself was killed at the hands of Touma. Calibur was apparently obsessed with reuniting the book to learn the secrets of the universe, but turned on the Sword of Logos because, apparently, Kento's dad caused the event before & was Calibur for five seconds & old Saber/ current Caliber thought he had been tricked by a traitor within the Sword. In that event, he'd been forced to kill him. Coincidentally, there is an actual traitor within the sword-- the lady from the Southern Base-- who suspects that Touma is suspicious & has tricked the other riders into believing that being alone with the Table of Contents in the other dimension has corrupted him & will force him to become the new Calibur. Calibur did leave his sword & driver to Touma with his final breath, but it magically vanished a moment later. In the end, the mysterious figure who gave Touma the King of Arthur book stopped them, announcing himself as a member of the Sword who wields the equal & opposite force to Calibur's sword-- the Sword of Light. But, he just transforms into a sentient katana, not a Rider. This seems to be what those working with the Traitor want, however. To get their hands on both the swords of light & darkness as the next step in whatever it is that they are planning.