It appears to be the monster being shuffled into the Deck as this card's effect's cost.
Below it are two monsters (from left to right) that have a rather strong resemblance to "Basic Insect" and "Hayabusa Knight" respectively.
This card's effect and name are arguably paradoxical. You first lighten your Hand by returning a Level 7 or higher monster back to your Deck, yet you then Draw a new card from your Deck, effectively retaining the same amount of cards in your Hand beforehand.
The same idea can be applied to your Deck, albeit in reverse; here this "load" is first made heavier with the returned card back in the Deck and then lightened to the Deck count beforehand after the card is drawn.
The term "lighten" is probably meant to be used in a functional sense, due to monsters of level 7 or higher being difficult to summon without the aid of other monster's effects.