Thanks for the chapter!
I hate it when explanations are lacking in detail. So the light that grants longevity, blessings on the land for abundant and healthy crops, power to the imperial family, etc. is really "The Mark That Magic Had Failed" which means what? If it's failed magic why is it giving off magic or something making things around better, or is it like a bleeding wound where the magic that should be used for some purpose is leaking out meaning there is less magic for the main purpose but do the nature of the magic leaking out it's boosting everything near the "wound"? Wonder if her cousin has a big crush on her but acting like a tsundere or jerk to cover his feelings and embarrassment. Be nice if he played that witch along and told the MC about the conversation but wouldn't be as interesting a story if he didn't listen to the devil's whisper so he's likely going to do something stupid and dishonorable. Witch really knows how to tell him what he wants to hear and he wants to believe her too much to notice all the holes in her story. Like is there any physical, concrete evidence giving credence to her lies or would MC really be his more so than before without the empire that she's only been in close contact with for a few weeks? Idiot should realize she only sees him as family and nothing else, and isn't going to change her views empire or not.