Tre, if you get this in time you should try a place called "Friends". It is a bit off the beaten path in Akihabara but their prices are amazing and all their games literally like new. I got Gimmick! CIB for 7,000 YEN, most of the old titles 1-600 yen, not 1,800 to 2,000 like the side road shops. I can tell which shops you went to from the stickers, as I lived in the area for some years. To get to Friends, go down the main street, the shop where you bought Icarus will be on the right(I'm thinking the shop you bought that from is the one thats near the crepe shop and it has a crane game out front with some high end items and some sleezy cosplay wigs on 2F, keep walking, eventually you will see a red coffee shop, I think Segafedo on the left corner. Cross to the side of the street that coffee shop is on. Now with the coffee shop on your right side(and a few blocks behind you an AM PM on the other side of the street), walk about 3 or four shops down. Friends has a little sign with Yoshi drawn on it that says the shop is on 2F. on 3F they have the newer games, Saturn etc. The place rocks. I literally bought my entire collection there over the course of two years or so. The loose Famicom games all have perfect white labels for god sakes... Place is sweet. Nobody knows about it though. If you see the old lady working there, tell her Mike says hi. Be weary of the younger geeky guy who works there though he literally flipped a brick when I asked him if one of their games in the clearance BIN was working or sold AS IS. I'm guessing at the time my Japanese wasn't good enough and I insulted in some way... Either way the older lady there is super nice so if you have any questions talk to her.
Sidenote, I once found 5,000 YEN laying on the ground in front of this shop after buying a Famicom AV and not having the spare change for a AC adapter and extra controller. This place is a place of the gods.
By the way not sure if you went there but Super Potato is shit and a tourist trap, prices are insane, staff is rude and most of their stuff is in shit condition. They grab it all from local flea markets for next to nothing, I've seen their staff hunting at them before. If you go to any mainstream place there go to Mandarake Galaxy in the Nakano Sun Mall, closest stop is Nakano Station near Shinjuku. Mandarake in Akihabara is also nice, bigger, etc. but prices are a bit higher as it's in Akihabara. They have a SICK selection of Megadrive games.
I think that it has "Retro Game" written in English on the window of 2F but not sure, Friends though is written in katakana and is the name of the shop. It's advertised super low key.