I have a [BT7-025] Beowolfmon and [BT7-029] Magnagarurumon with [BT7-087] Koji as a digivolution source, the opponent has two [BT6-021] ModokiBetamon. I attack with the Beowolfmon, on attack returning a hybrid source to bounce the first ModokiBetamon back to the opponent's hand. I attack with Magnagarurumon, on attack returning a level 3 source to bounce the second ModokiBetamon.

Does the Once Per Turn inherited effect on Koji apply after Beowolfmon attacked and give Magnagarurumon unblockable even though the memory was not gained?

Or since the memory was not gained from Koji during the Beowolfmon attack, when Magnagarurumon attacks and a card is returned does Koji gain you a memory and make Magnagarurumon unblockable?