This is a collectible telephone card that was awarded to Young Animal readers through a lottery. It was issued in May 1999. I'm not sure how many were available and I'm not willing to rummage for the issue of the magazine that would have that information at the moment, sorry. It usually ranged between 50 and 200.
This card was used to advertise a "manga challenge" that was running every month in the magazine at that time. What makes it especially interesting to us is that the illustration (Puck playing with a dragonfly) is quite rare. As far as I recall, it was never featured anywhere else.
By the way, for the younger generations: these cards were used with payphones. At the turn of the 20th century, telephone booths were available in public spaces so people could conveniently place a call.
These originally used coins, but had a tendency of being vandalized, and so in the 1980s phone cards were introduced to alleviate the issue. Their use dwindled in the mid-2000s, when the prevalence of mobile phones rendered them obsolete.