Where your soulmate and you spark (it feeels like joy, it doesn’t hurt) when you touch the first time. It’s enough to clearly be seen, but only is about the size of their palms.
The sparks return even more intensely when the two are completely in love and the relationship is healthy. The sparks cover wherever you touch.
The longer you have the spark, the better you get at controlling them, bc always having sparks is like bragging. Being able to surge sparks at will takes at least 5 years of practice to master.