The Arcmage's Reluctant Heir

Wren Aldiss was running a failing charm stall in a grey corner of the market when the greatest archmage of the age walked into her shop, sat down on a stool, and refused to leave. Three days later Ilse Vantorre was dead, and her will named two heirs: Wren, and Ilse's grandson Merrit, who has spent his whole life expecting to inherit. The clause requires them to share the tower for a full year. Merrit does not have his grandmother's magic. He has his grandmother's duty. Wren has both, and a shelf of notebooks Ilse wrote for her specifically. An OP MC progression fantasy romance for readers who like their overpowered heroines patient and their inheritance complicated.