bud
蓓 centers on the early stage of a flower: a bud, the compact form before blooming.
蓓 is a phono-semantic compound with 艹 (grass/plant) as the semantic component and 倍 (bèi) as the phonetic. It originally referred to a flower bud.
The grass radical 艹 sits on top of 倍, which can be thought of as a plant doubling in size. Imagine a bud on a plant that will soon double into a full flower.
For ハイ, picture a bud saying 'Hi!' as it peeks out from the plant: Hi -> ハイ.