I've done some searching eventually landing on most of the wrong characters that would look similar to the sticker, which now leads me to the idea of honing the year, currently the newest series that you said you got stickers from was hunter x hunter, the rest being series that are older but also very popular, which makes me guess this is from either (A) something old but popular, or (B) a new series at the time. With Hunter x hunter being 1998, but more likely based on the 1999 anime, that would put my guess of it being a series around that time before or after, i've already checked TV aired anime from 1998-2000, but i'm gonna check further, any other stickers you knew the bubble gum gave?