KanjiJLPT N2
Transparent

transparent, permeate, filter, penetrate

Mnemonic

Walking down a path, you meet a monk who excels at meditation so deeply that his body has become transparent. You can see the path right through him! The more he excels, the more see-through he becomes, until only a faint shimmer remains.
Additional thoughts
Picture a glowing, see-through figure sitting cross-legged on a forest path — the trees and stones visible through his body. Spiritual mastery (excelling) leads to transparency.
Quick recall
A monk on a path who excels at meditation becomes transparent.

Details

The keyword for 透 is transparent. This kanji conveys the idea of something being see-through, clear, or allowing light to pass through without obstruction. It carries the sense of translucency and clarity, as in objects or substances that one can see through. By extension, it can also suggest permeation or penetration, as something passing completely through a barrier or medium.
On'yomi
とう
Kun'yomi
す.く、す.かす、す.ける、とう.る、とう.す