Shoubu (しょうぶ、菖蒲) are iris leaves. The kanji is homonymous with 勝負, meaning “victory or defeat” - that is, a battle, a symbol of spirit to meet challenge. Customary on Children’s Day is to place shoubu above the house entrance (as are now on mine, though my children have long departed) and to have children bathe with them in what is called a 「しょうぶ湯」- “shoubuyu,” or “iris bath”.
Kumanichi notes that local sentos (銭湯、public baths) offered free admission to children on 5/5 and provided a cute photo. These baths were crucial after the quakes, admitting free those with no water or gas. If you’ve never visited a sento, you should. Here is a link to local sento. -William https://tinyurl.com/y2uqzvu8
