Kingdom Hearts vs Mega Man
Connection:
Both are inhuman clones of their series' main characters (Roxas being Sora's Nobody and Axl being a Reploid aka, a replica of X), who's lives started with the team that for a while, they would call home (Organisation XIII and Red Alert respectively)
Both were disturbed by some of the ruthless and inhumane actions of their teams, which were the results of a bald-headed immortal puppetmaster (Xehanort in Roxas' case and Sigma in Axl's) manipulating them to utilise a unique gift that both possessed (Roxas' Keyblade and Axl's copy chip respectively) in order to further fuel their immortality through collecting what was effectively their series' fancy versions of souls, as well as make vessels for them to constantly return (Organisation XIII collecting hearts and acting as new incarnations of Xehanort so he can forge the χ-blade and a bunch of other complicated shit, while Red Alert collected DNA souls that Sigma tricked their leader into feeding to the various members that ended up corrupting them with the Sigma Virus).
Both attempted to run away from said organization until they were captured immediately afterward by the main character's best friend (Roxas being captured by Riku and Axl being captured by Zero). Ironically, both being stoic swordsmen that are frequently corrupted by the main villain but still stick with Sora and X through thick and thin
Both would also be forced to put down a fellow team member they saw as a friend (that happened to be a clone of the same person) who on the surface seemed to be trying to take them back by force but were in fact trying to save both from a dark fate (Xion seemingly being reprogrammed to merge with Roxas to make a Sora clone the Organisation could use without issue, but in truth just sacrificed herself to Roxas to foil Xemnas' plans, while Red seemingly challenged the Maverick Hunters so he could get Axl back but in truth, he was trying to let Axl go so he wouldn't get caught up in Red Alert's downfall but was blackmailed by Sigma into getting Axl back anyways)
Both were given by Riku and Zero respectively a tool they would use in the final act of the games these happened in, with Roxas battling through The World That Never Was with his new Synch Blade ability and Axl using Red's DNA soul to kill Sigma)
Both would eventually find a happier life with a new bunch of friends, but would meet tragedy not long after (Roxas merging back with Sora and seemingly dying and Axl being knocked comatose by Lumine, with his fate left unknown), though both would be back from this not long after (Roxas being brought back in KH 3 and while in mainline MMX, Axl's fate hasn't changed, the spin-off Command Mission (which is set 100 years in the future) sees him still around despite this), and they would find themselves fighting alongside the ones they were cloned from, their stoic swordsmen buddies and several others working to vanquish the evils of their world (the Heartless/Nobodies and the Mavericks respectively (both beings evils that are created through innocent people being corrupted by a malevolent force (the Darkness and the Sigma Virus respectively))
Both worked alongside and later fought a character with their same unique ability (Xion and Redips respectively), share a fighting style with other members of their cast (Roxas fighting like Sora and Axl fighting like X in X7 and Bass in X8), dual wield their respective weapons (Roxas' Keyblades and Axl's pistols respectively), were shown the ropes by and frequently worked at first with a red teammate (Axel and Zero respectively), are parts of a trio (Roxas with Axel and Xion and Axl with X and Zero), are both exceedingly naive and even stubborn and made their full debut on the PS2 (Roxas making his first full appearance in Kingdom Hearts 2 and Axl first appearing in Mega Man X7). And there's also a battle of opposites motif too, given their polar opposite core personalities-Roxas being moody and introverted while Axl is loud, proud and eager to rush in head first
