Lan Xichen continues to carry all the books of the Lan Clan with him in a qiankun bag sewed to his robes; it is soothing to know that they're there, and (he thinks) if he is captured they'll lose regardless, so there is little point to keeping the books separately. But the books aren't what he's been reading in spare moments. No, he's leading a war, and so he's been reading Sun Tzu:
Amidst the chaos of a sea of flags in the battlefield, order must be maintained. Even when the view is unclear, adherence to an army’s formation will ensure it cannot be defeated. Yet, disorder can arise from order, fear from bravery and weakness from strength. Orderliness can be fostered via coordination, bravery via the impetus of a situation and strength via training.
He had never quite realized before how much coordination was involved in fighting wars. He was the First Jade of Lan, with high cultivation, skilled with a sword and a bow, but these days Shuoyue remained sheathed. He busied himself with troop movements, camp locations, guard rotations, staffing of hospitals, and always and everywhere food. Food, Lan Xichen had discovered, was very important for fighting wars. He could only imagine how important it would be if half his army wasn't capable of inedia.
Nie Mingjue grew bored easily by this sort of detail. As far as he was concerned, "strategy" meant figuring out where the most Wen were, and "tactics" was charging at them with sword drawn. Lan Xichen viewed his childhood friend with fondness, and left him to lead the troops into battle. Lan Xichen missed Meng Yao, who loved maps and charts and account-books with the passion that Lan Xichen reserved for the xiao, and who had a perfect memory for which commanders had good instincts, which were too brave for their own good, and which had powerful families and so had to be assigned to some location where their honor could be intact without them having a chance to do much harm.
And-- Lan Xichen would be honest-- he missed the deftness of Meng Yao's fingers and the softness of his skin and the delightful pleasures he had introduced Lan Xichen to, ones Lan Xichen had never before thought of, that were not forbidden by the thousand rules of the Lan Clan, perhaps because Lan An had never thought of them either. Lan Xichen had, in his turn, introduced them to Nie Mingjue, but it was not at all the same. At night Lan Xichen had many exciting anticipations of the war being over so Meng Yao and Nie Mingjue could cooperate in making them more... exquisite.
Lan Xichen was bent over a letter, writing this humble servant is surely mistaken and meaning fuck you asshole, you promised us two hundred strong cultivators and where the fuck are they, when a hole in the floor opened and he disappeared.