Li smirks at Koutarou's reply. "That is a good answer. You may have much more insight to the matter than most. The answer I expected would've been 'because Hollows are our enemies!'. For your curiosity, here is what we thought thousand years ago, when I was just a lowly intern building the Central Hospital:"
"The Court Guard was founded to prevent a war between Noble Families. Yet, in fifty decades, no military threat, internal or external, has appeared. As such, we of the Central 36, chosen amongst the wisest men of Rukon and Seireitei alike, demand that to make up for the costs of its upkeep, as a peace-time duty every member of Gotei 13 resume the most holiest of duties of Shinigami: that of purifying Hollows and guiding lost souls to their deserved resting place."
Li extends a hand and offers the parchment for Koutarou to read. It most likely is not the original, but it is still written in archaic form of Kanji.
"Peace-time duty. That is what we considered it back then. The thought of an army of Hollows would've been nonsensical to most of us at the time. 'Do you call a pack of wolves an army now?' would have been the question most would've asked when faced with such a concept."
Li starts flipping through pages of the book again. "There were much fewer people back then, and correspondingly much fewer Hollows. All the supremely powerful Hollows of myth had already been dealt with at that point. But for contrast, do you want to know what kind of relation we had to Hollows when the Academy was found? Or before the Academy was found?"