Well, it depends on how illogical a gag you want...
First, they can work by logical stages, which means puchis turn into either destroyers or their "adult" stages, which means BBs for those two. (Insert RJ scream of despair here.) This basically assumes puchis are just babies, though.
The second option is that puchis are entirely separate organisms, so they turn into old and wrinkly puchis, which causes Tenryu's head to explode.
KongouDeesu!What's going to happen!Okay then...!
Firing Beam !助けて!Hiee!DeeeeeeeesuI've really done it now!dmpdmpdmpWhoa, Kongou.... That's an amazing look there.KongouAdmiraaal!
Turn me back quick!Hehehee...
Kongoh-chan's so cute...ヘイー! Admiraaal!
I wanna turn back!There's nobody around? ...right?Hieeeeeee