I used to do this activity as a card exchange game followed by taping the cards to the students' backs for them to guess their identity, but doing it as a group activity requires less management and runs a little smoother, I think. If you'd like to do it by taping the cards to their backs instead, you can definitely change this to do so, just be warned that it gets VERY busy.
First, introduce the ten school subjects and have the students practice saying all of them. Calligraphy and home economics tend to be the problem spots, so make sure they can say those two in particular before the later activity.
After this, I have some pictures of famous characters attempting to study some school subject. Have the students look at the pictures and tell you what they'll studying. I'm pretty confident in my assessment of what subject they're studying for all of them except for Godzilla, which could be anything, but I said social studies because Godzilla likes learning about all the different places in the world he can destroy.
Next is the main activity: Forehead Cards. Show them the instructions in the PowerPoint (written out in Japanese, so it should be extremely clear to everyone). First, they'll move their desks together into groups. Then, you'll pass out one deck of cards to each group (see attachments; you'll need to make and laminate these beforehand; I usually make one deck 30 cards and enough for 10 groups, meaning laminating and cutting out 30 sheets, but it's up to you if you don't want to do that many). Additionally, there's a grammar sheet you should pass out (one per student is better, but at least one per group) which they can look at if they can't remember the English sentences. Have the students shuffle the cards before they start. Then, they should do rock, paper, scissors to decide who gets to take a card. The winner should take a card from the bottom of the deck instead of the top (since you can see through the top a bit) and put it directly onto their forehead without looking at it themselves but showing it to their group members. Then, starting with the person sitting on their left and moving clockwise around the group, the other group members tell them the hints on the card. After all the hints are read, the person has ten seconds to say which animal card it is. If they're correct, they can take the card and receive one point. If they're incorrect, or ten seconds pass and they haven't answered yet, they return the card to the deck. Then, the group should do rock, paper, scissors again to see who gets to do the next attempt. The person who gets the most card at the end of the time limit (I usually set it at 15 minutes) receives a sticker (or stamp or whatever reward you want to give them).
I've used my picture in the instructions for this, so you'll have to change that to yourself (or clipart or something) before you show the PowerPoint to the students.
I've included a lesson plan written in English and Japanese, so your Japanese homeroom teachers can read it and know exactly what the plan is.
The font used in this is UDデジタル教科書. It should be on all of your school computers, but I don't have it on my personal computer at home. I prefer it because it has the handwritten lowercase "a" as well as other handwriting differences, but doesn't look like garbage like Comic Sans. If you don't have it, there might be some formatting discrepancies.
Credit to the respective copyright holders for use of the characters' pictures.
Credit to flaticon.com for the use of the icons.