User blog comment:B214/Volume 23 discussion blog/@comment-185.112.105.215-20170429113028/@comment-30048084-20170430201658

If they want to marry her they have to beat her at chess or I guess a rating considering how full her peerage is, either way it is impossible to force her

if it ends up a rating game if you exclude all the Artificial Sacred Gear wielders she has Tsubaki, Saji(Vritra), Bennia and Rugal. No chance of victory unless it is a fight with an Ultimate-Class's Peerage.

Plus Serafall may be sealed but that won't be forever and if she hears that So-tan is in danger Trihexa battle might end a lot quicker