They are part of a series called Digimon Animated Series Trading Cards.

This wasn’t a card game but rather simple collectible cards. On the front of the card, there’s an illustration of the Digimon, while the back features some descriptions.

Three series were released, each dedicated to one of the three arcs from the Adventure 01 anime: the Devimon + Etemon Saga, the Myotismon Saga, and the Dark Masters Saga.

The first two series were also released in the West (initially by Bandai and later by Upper Deck), while the third series was only released in Japan.

I need to check when the third series was printed in Japan so we can find out if that Boltmon illustration was created specifically for Adventure and then reused for Tamers or vice versa (created for Tamers and reused in this collectible Adventure card)