Update 11/15/13: Prices listed below are not correct as they raised their prices earlier this year. The increase wasn't much so everything is still quite affordable and cheap compared with a lot of other Japanese restaurants in Boston.
Pikaichi, located at 
1 Brighton Avenue, Allston, MA, in the same building as Hong Kong Supermarket (formerly Super 88 Market), is a Japanese restaurant specializing in 
ramen, 
curry (karē), and 
donburi. It's basically a little piece of heaven.
Pikaichi took over the space where 
Ken's Ramen House used to be. 
José Garcia told me that when Ken decided to move back to Japan, he sold the business to Taka & Ritsuko Akatsu, the former owners of 
Café Mami, who in turn sold their business to José's brother, Carlos. Yes, the restaurant dishing up Japanese comfort food is owned by a Guatemalan. :)
I never went to Ken's, so I won't be comparing Pikaichi with its predecessor. What finally got me over there a few weeks ago was a friend from Japan telling me she'd been there for the first time and felt like she'd just been to Japan. It's been so long since I was last in Japan that I don't actually remember if I had ramen and if so, what it tasted like, but I know a good bowl of noodles when I taste it. 
The first thing you'll notice (probably at the same time as you take in the amazing smells) is that the staff are very perky and you'll be greeted enthusiastically with a loud 
irasshaimase!  I was a little surprised the first time I went since you don't hear that at too many Japanese businesses in Boston.  They play only Japanese music (seems to be all 
J-pop and rap) and the waitstaff speak in Japanese, although some of them can speak English fluently, so if you have questions about the menu but can't speak Japanese, there should be someone there who will understand. I can see why my friend felt like she'd been to Japan.
So far I've only eaten ramen there on days that weren't ridiculously hot, but they're well air conditioned so you could comfortably have a bowl of ramen on a 90 degree day. Pikaichi's noodles comes from 
Sun Noodle (they have a 
factory in NJ but are a Honolulu-based company). Here are 
pictures from a visit they made to Pikaichi. According to the signs on the tables, Pikaichi serves 6 oz. of noodles (5 oz. is industry standard).
I always get the Tokyo Shoyu Ramen with corn ($7.99 + 50 cents). It's the best ramen I've had in Boston. Maybe some day I'll branch out and try one of the other varieties, but I really like 
shoyu ramen.
|  | 
| Tokyo Shoyu Ramen with corn & half egg, no scallions + small curry rice. | 
I also love that you can add a rice bowl of curry rice to an order of ramen for $1.99! (You can also add a small bowl of 
cha-shu don for the same price.) Note: the small curry rice is only available in regular. When I requested medium hot, they brought me a bottle of 
Sriracha and said I could mix it for the right flavor!
Today I tried the 
Tatsuta Curry Rice ($8.49). All curry and 
donburi come with a bowl of miso soup and at lunch Monday-Friday, a free small salad that has mixed greens, corn, and house dressing which I think involves sesame oil, soy sauce, ginger, and some other stuff. (You can also add a free small salad or bowl of rice to an order of ramen at lunch Monday-Friday.) It's nice to have some veggies and the dressing is tasty, but the salad is just okay. I can't comment on the miso soup because I'm 
allergic.  (I know, how sad is it to be Japanese and be allergic to soy? I developed the allergy in my 20s. Fortunately I'm still able to have soy sauce and other soy products without incident, just not 
edamame, 
tofu, or soy 
miso. There are companies in the U.S. that make non-soy miso but you'll never find them in an authentic Japanese restaurant. The thing I miss most is 
inarizushi. :( If you have dietary restrictions or allergies and are going to Japan, 
Just Hungry has a great
 set of food restriction/allergy cards you can print and carry with you.)
|  | 
| Tatsuta Curry Rice with miso soup & free salad | 
Pikaichi's curry is delicious. The medium hot is rich and spicy without being overwhelming. There's no burn, just a nice kick. The regular has the same rich flavor but no kick to it, so unless you're really spice-averse, I recommend medium hot. I haven't tried hot since I expect it will be too hot for me. I grew up eating curry at home which my mom made fairly chunky with potatoes, carrots, and beef (no onion for me). In restaurants it tends to be more about the sauce with only a few bits and pieces. You'll find some very cooked down onions and a few small pieces of chicken and/or beef in the sauce and that's it. A plain curry rice might not satisfy if you're a big eater since it's just a lot of curry sauce and one serving of rice.
I've gotten a curry meal twice and find that the rice to curry ratio is off and I always need more rice. I've asked for extra rice both times and not been charged for it. I had expected to be charged for it because it's on the menu as a side ($1.50), but maybe that's if you're just ordering it with ramen.  
The chicken tatsuta was delicious and juicy. It was tasty on it's own, but overwhelmed by the flavor of the curry.
|  | 
| Tatsuta Curry Rice | 
A note on 
daikon. I had a love/hate (mostly hate) relationship with 
daikon when I was a kid. If prepared incorrectly, it's very bitter, and not at all tasty. I tended to like it overcooked in miso soup. I only recently learned that 
daikon is 
served with greasy Japanese food to aid digestion. That's why it's in the 
tentsuyu (dipping sauce) served with 
tempura. So the bright red 
fukujinzuke on your plate isn't just there for decoration. Eat up!
I was taught that after a meal, you should return disposable chopsticks to the wrapper (if you didn't already make a chopsticks rest out of it). This is confirmed by 
Etiquette Scholar but according to 
JREF, it's controversial. (For more chopstick etiquette, see 
Just Hungry's guide.)
I think the most disappointing item I've had at Pikaichi was the Cha-shu Salad ($4.99), but it wasn't that it was disappointing, it just wasn't amazing compared to the other things I've had. It's a very basic appetizer-sized salad with mixed greens, corn, cha-shu (Japanese 
char sui), scallions (which I skipped), and house dressing. I also suspect their 
takoyaki ($5.49 for 6) are of the frozen variety, but I didn't care. They were warm and delicious and the 
tako chunks were a decent size.
I got their ridiculous sundae ($4.99) once. Two scoops of vanilla ice cream, flan, chocolate syrup, frosted corn flakes, and frozen raspberries. I must have looked really cold while I was eating it because one of the waitstaff came and asked me if I was cold and did I want some hot water. Lol. For some reason I had expected the raspberries to be room temperature so the frozen raspberries were a nice touch. The sundae was way too much sugar for me all at once but it was delicious.  
Note that they close between 4:00 - 5:00 PM so their staff can eat dinner and have a break.  My friend and I didn't know this and showed up at 4:45 PM once, so we went shopping in the market to kill time.