Heungmakgwa Sagwindani Ohaeindeyo

Enter Heilbronner: gentleman thief! The main villain of a novel, who fought against the heroes, steals from the rich at night, but by day takes on the identity of Ludger Kassen, the philanthropic son of a duke, more interested in history than politics or power. As commander of the ragtag Ruby Knights, isekai’d knight Clara has no choice but to get involved in the Heilbronner case. However, in doing so, and in working alongside Ludger himself, Clara learns he secretly has far grander motives...
(Source: Tapas)