>>279787699There isn't NEARLY enough of the two tomboys without Koyomi showing up. Hell, there's not enough of the Fire Sisters without big brother tagging along, either. Just give us yuri, you fools.
>>279790475You're not looking for an absolute number, but a differential from your own. Who wants to be a 57-year-old with a 13-year-old little sister?
I'd say about 3-4 years younger is ideal. Long enough to lord it over her,close enough that you're in your prime to enjoy her cuteness.