Unusual Mark On Kissaki Of Sumitani Tachi

[terminus]

Hi, I saw this sword from Sumitani Masamine and everything was perfect except this unusual mark on both sides of the kissaki. Does anyone know what it is? (a flaw? on purpose?) and what might of physically caused it? 

[lonely panet]

maybe some core steal???

[Mark]

looks like chikei or similar activity

[terminus]

I was thinking it might be chikei but seems way to large to be it. Core steel.....maybe but how does that even happen on the kissaki's outer layer? 

[brannow]

Hi I also think chikei or inazuma.

[Marius]

The smith has probably used different kinds of steel and this is the result. I got a somewhat similar thing in a tanto blade...