Okay, this is a serious level of sweet mixed in with the typical tropes. I'm liking it. It's a good thing that mc just wants things to be resolved without genocide (on either side). He's not giving the naive vibe, more like just keeping peace because it means less death and/or revenge for everyone.
Though I also feel like the current world could use the threat of a dragon barely being contained by a peace loving older brother. "Stop hurting each other, or I really won't be able to convince this cute little dragon sister of mine that your lives are still worth sparing"