Daihasei Festival Arc (Index)

The Daihasei Festival Arc is a story arc in Toaru Majutsu no Index. It is September 19th, and the time has come for Academy City's annual Daihasei Festival, a sporting event that pits ability users from across the various schools of the city against one another in a series contests. For Kamijou Touma, this year's festivities have come with a twist as he finds himself having to foil a plot that could wreck the fragile balance between the worlds of science and magic.

The arc marks the 2nd time the Roman Catholic Church acts as the primary antagonist for Touma, it involves the church allowing Lidvia Lorenzetti to take over Academy City for the benefit of the church using the Croce di Pietro.

Increase of hostilities in the Magic side
With the destruction of their main fighting strengths: the Gregorian Chant and the Agnese Forces, as well as with the Amakusa Catholics and Orsola Aquinas joining the Anglican Church (due to the events of September 8), and with the balance of power gradually shifting to the Science Side, the Roman Catholic Church has become severely weakened enough to allow the Mardi Gras – Lidvia Lorenzetti – to set up the Croce di Pietro in Academy City and take it over in secrecy. With the church suceeding in taking control of Academy City, would cause the power balance to shift to the church's favor since Academy City is the center and the entirety of the science side.

Her reason being in ensuring the welfare of the world as she views the Science side is ursurping God's will, as well as her innate desire to conquer a difficult challenge, which is in this case taking over Academy City for the Roman Catholic Church and evangelizing it's inhabitants under it's dominion.

Oriana Thomson a is later involved with the operation, under the belief that having the Roman Catholic Church control Academy City, would create an absolute standard concept regarding goodness, due to it being governed by the laws of one unifiying belief. Since the concept of good being dependent on a human's perspective towards it, which often cause tragedies since it becomes twisted due to the nature of humans. Oriana sides with the Roman Catholic Church since they are the most capable of achieving her goal, through the dominion of others.

Trivia

 * This arc would mark the first time an arc covers two novels.