Tensei shitara Koutei deshita: Umarenagara no Koutei wa Konosaki Ikinokoreru ka? @comic

"I command thee, kneel!" When a history buff reincarnates as the infant emperor Carmine, he's immediately struck by despair—child rulers aren't known for their longevity. But as he learns the ins and outs of his new reality's elaborate metaphysics and "his" corrupt and bloated state apparatus, he sets in motion a scheme to purge the rot—and woe betide any scheming noble standing between Carmine and a functioning government. Of course, he'll have to survive first—no easy feat for a child emperor dancing on other men's strings. But hey, how hard could running an empire be? (Source: J-Novel Club)