Ok, lets just forget for a second that Mega Man is WAAAAY fucking older than Kamen Rider W, lets go into the realm of What Ifs here.
What if, after the destruction of the Sonozaki mansion, someone found the Gaia Well (or whatever its called). Lets say that someone decided to use that Gaia Memory technology to create incredibly advanced robots, implanting them with Earth's memories on one specific thing. This is where we get enemies like Flash Man (Flash Memory), Heat Man (Heat Memory), and what not.
I mean, think about it, these robot masters are just too....specialized. What if they are actually techno-dopants.
Megaman himself is like a walking Lost Driver, able to steal the Gaia Memories form the robot masters and use them in his own systems.
I don't know what to say, usually I only see Decade being linked with Megaman in terms of abilities(acquiring and using other's riders and whatnot.) And how he acquires them, by killing them off before he gets the abilities.