The kanji 益 visually depicts a container (皿, dish) with something **overflowing** or **increasing** from it. This abundance represents a **benefit** or **gain**.
'Masu' — You want a **MASS**ive **benefit**, right?
'Eki' — Sounds like 'E.K.', as in 'Extra Kash' (cash), representing **profit** or **gain**.