Evidence (The 2nd, 3rd, and 4th pieces of evidence are most interesting IMO):
- They look very similar...
-Same Skin Color
-Same Curly Hair
-Same body build...large upper body, small legs
-Same square jaw. - Kuma is known to be of a different race, and Blackbeard has a "weird body." That might mean he is of a different race as well.
- Kuma technically had 2 devil fruits in Kizaru's replicated light fruit and his original paw-paw fruit. Blackbeard does as well.
- Kuma never slept while protecting the sunny and Blackbeard doesn't sleep either.
- Kuma hates the government, and its speculated that Blackbeard wants to overthrow the government and be the new king of the world. Maybe they have a similar reason to hate the government related to their race.
- Blackbeard and Kuma are both orphans - might be connected.
- Blackbeard caught Bonney and asked her to be his woman. She seemed to hate him. Maybe there is a connection between the two or this is setting up a future plot point?