Adoption in anime is always an interesting theme. From what I have seen, the theme is largely ignored, and is mostly a plot device of sorts. It receives no further treatment, exploring the minds of the adoptee and adopted.
Ponti-dono speaks of Mari acting as a de facto mother for Mirai in TM8.0 and how this relationship practically mirrors Balsa from Seirei no Moribito (though I’ve never seen the show).
What I was interested in was how race and ethnicity play into the psychology of adopted characters in anime. One good example is Eureka’s kids. [warning, Eureka 7 spoilers follow]. The reason why a transracial – hell, it was trans-species – adoption seemingly, seamlessly works in Eureka 7 (Linck was black). One guess is that the complexities of transracial adoption is neglected for the sugarcoated kazoku theme that permeates a lot of anime. This is very similar [warning, Nanoha spoilers follow] to Fate, where Admiral Lindy adopts fate, though I’d say the adoption focused more on the development of Fate than it did the relationship between Lindy and Fate – Lindy was also a single mother. Yet in Nanoha, race, ethnicity and nationality are non-issues, despite the existence of different “worlds” made explicit. It’s just for marketing, yeah, but still.
But, probably the most interesting case is in Dragonball Z. Goku was a saiyan, yet he was adopted by a human. This gets complicated when Vegeta shows up and Goku’s saiyan identity is propelled by Vegeta. Throughout the anime (I wouldn’t bother with the manga….) Goku does acknowledge himself as Kakarot, but fights Vegeta not for any racially (saiyan vs. human) motivated reasons. For Goku, it’s more of those ubiquitous themes of HEROIC JUSTICE etc. which motivate Goku to fight. On the contrary, Vegeta’s discourse is situated in the intersection between class and race (the prince of saiyans) – that’s why he’s always flabbergasted that a “common soldier” could be stronger than a royalty.
Of course, while race and class are addressed somewhat in DBZ, Goku’s mentality is ignored for the most part. In most real life cases, as there is a bit of literature on the subject, transracial adoptees will suffer from any number of theoretical psychological constructs, double consciousness, multiple selves, cognitive dissonance, the other, etc. This is the kind of complex issue I haven’t seen in any anime that does feature interracial adoption.