Best Hiro freebies are Adzan's clothes at DAZ Freepository forum. Going through PoserClub.jp may bring some very nice faces and clothes too (school boy uniform, swim trunks). Rendo freestuff has Sarasara2 hair made especially for Hiro. I'd dig through my treasures to list all freebies for Hiro I have but unfortunately I'm not at home, where my rendering machine and all the archives are :( Hope this makes a nice starter though :)

Edit: don't forget about H3-D3 hybrid that comes with Hiro (Hiro's head on David's body). This way you can use David's clothes if you have any - and if not, go and get D3 Imagination Gown at DAZ weekly freebies archive, apart of that silly hat it's a very versatile outfit.

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Outdated gallery over at DeviantArt

Fics at FanFiction.net and Archive of Our Own (AO3)