The safest route might be little change at all--since (if language teachers are to be believed), years later you can find yourself calling your high school senpai, "senpai" and your childhood friend "1stname-chan" and your college friends "lastname-san". Perhaps just dropping the honorific when things get *very* close.
Glancing at a few random Slam Dunk doujinshi, people can stay with last names even when being *ahem* very intimate. Also, a change to a first name or to plain last name might only occur in extreme, isolated circumstances, with the last name or last name+honorific being used in everyday life.
(I'm assuming you've got all the Confucianism-hierarchy, know-your-place etc etc stuff from googlings.) Often people who are very "proper/upper class/formal" will stick honorifics on, even when addressing someone lower, hierarchy-wise. For example, a very refined mother to her child, although clearly the child is below the mother. Close friends and people who tend to be more disrespectful/friendly may drop the honorifics where a less presumptuous person wouldn't.
If you aren't on it/haven't heard of it already... a good place to ask about this stuff might be the AMLA (http://groups.yahoo.com/group/amla/). It's a general yaoi/BL ML (with leanings more toward "intellectual" than "squee"). Not everyone there might be a fan of Prince of Tennis, but there are people there fluent in Japanese (and interested in 2 guys together) who could probably help you out or point you someone who could.
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The safest route might be little change at all--since (if language teachers are to be believed), years later you can find yourself calling your high school senpai, "senpai" and your childhood friend "1stname-chan" and your college friends "lastname-san". Perhaps just dropping the honorific when things get *very* close.
Glancing at a few random Slam Dunk doujinshi, people can stay with last names even when being *ahem* very intimate. Also, a change to a first name or to plain last name might only occur in extreme, isolated circumstances, with the last name or last name+honorific being used in everyday life.
(I'm assuming you've got all the Confucianism-hierarchy, know-your-place etc etc stuff from googlings.) Often people who are very "proper/upper class/formal" will stick honorifics on, even when addressing someone lower, hierarchy-wise. For example, a very refined mother to her child, although clearly the child is below the mother. Close friends and people who tend to be more disrespectful/friendly may drop the honorifics where a less presumptuous person wouldn't.
If you aren't on it/haven't heard of it already... a good place to ask about this stuff might be the AMLA (http://groups.yahoo.com/group/amla/). It's a general yaoi/BL ML (with leanings more toward "intellectual" than "squee"). Not everyone there might be a fan of Prince of Tennis, but there are people there fluent in Japanese (and interested in 2 guys together) who could probably help you out or point you someone who could.