Hanamuko No Yakusoku summary:

Till death us do part. A solemn wedding vow, and one Lord Deverell's young bride ardently wishes to bring about - sooner rather than later! Only minutes after the wedding, Alexandra is brandishing a pistol at her husband, accusing him of ruining her father and killing her brother. So Deverell makes one more, wholly unexpected, vow: that he's completely innocent of both crimes and will prove it.