Bike registration

My friends who was in Japan left me his bike.
I was told that without registration card (or however it's called) I might have problems with the police.
My question is what do I need to register bike in Japan, my friend left me only a manual and keys but not any receipt or a proof of purchase.

Misha,

He should have made a note with signature mentioning he is giving the bike to you. Then you could have taken the note to the police to have it registered for you. Either way, visit your nearest koban and ask the policeman what you can do. It would be safer to bring your cell phone and be prepared to call the original owner from the koban in case anything gets complicated.

Very easy process, you hopefully are still in contact with your friend, have him write out a paper transferring the bicycle to you, and sign it,make sure you put the bike serial number on it, he can probably sign it, scan it and email it to you. Take that with 500 yen to a bike shop for re-registration, costs like 500yen.

I have the EXACT copy of the text form I used:

You can probably copy and paste it from below:
---------------------------
自転車者譲渡証明書
TRANSFER OF BICYCLE OWNERSHIP
譲受人
NEW OWNER
名前_____________________________________________________________
NAME
住所_____________________________________________________________
ADDRESS
_____________________________________________________________
電話______________________________________________________________
TELEPHONE NUMBER

-------------

譲渡人
PREVIOUS OWNER
私はこの自転車の正当な所有者であることを保証した上で譲受人に譲渡したことを証明し
ます。
I TRANSFER OWNERSHIP OF MY BYCYCLE TO THE PERSON MENTIONED ABOVE.
名前_____________________________________________________________
NAME
住所_____________________________________________________________
ADDRESS
_____________________________________________________________
電話______________________________________________________________
TELEPHONE NUMBER
車体番号__________________________________________________________
REGISTRATION NUMBER
カラー____________________________________________________________
BICYCLE COLOR

sorry the formatting is not correct, just make sure all that information is there and you should be ok. I recently sold my bicycle and used that form.