Black Clover Gaiden: Quartet Knights manga summary:

Its black clover spin off form shonen jump + the story based on the black clover ps4 and pc game quartet knights by Yumiya Tashiro of Night King and Dragon's Dogma Revives fame!

Yami Sukehiro, the captain of Asta's knight order, the Black Bulls, suddenly grows younger, just as a mysterious mage launches an attack on the Clover Kingdom. Join Asta and his friends as they embark on a new adventure of trials and tribulations.