Forum:Thunder King Rai-Oh effect

The rulings for Thunder King Rai-Oh's second effect says that a person can only negate a special summon that do not start a chain. I am confused by this because I think that pretty much anything can be chained to by something.

I would like to know what kind of special summons do not start a chain and if I am able to negate this special summon as soon as it happens or if I would need to wait until my main phase to negate it.