The fourth character is the idiom of "Maru", and the four-character idioms and explanations of the last character ending with "Maru":
Sakagami Zumaru - Sakamaki: Slope; Maru : projectile. Like a projectile rolling down a slope. It is a metaphor for the rapid development of the situation or the smooth progress of the work.
Shimohan walking pill - Han: slope; pill: projectile. Roll the projectile down the slope. A metaphor for speaking quickly and fluently.
Draw Ogawa Maru - to praise the mother for her good teaching of her children. Same as "Drawing Ogimaru Bear".
To take a pill against the odds - a metaphor for things being difficult to accomplish. Same as "Reverse Sakazuki Pill".
Rolling the pill against the slope - rolling the pill against the slope. Metaphor that things are difficult to do.
A projectile that escapes the hand - describes the roundness and smoothness of the poem.
Shimotsaka Maru - a projectile rolled down a hillside. It is a metaphor for following the trend without any hindrance, being agile and without stagnation.