Hijiki ひじき is one of the several "kaiso" 海藻 or sea vegetables (sounds better than "seaweed") which has been a part of Japanese cuisine for a long time. Japanese consider hijiki to be a healthy food with high fibers and minerals. As I was growning up, we had hijiki occasionally, but it was, by no means, my favorite dish as a kid. It does make a nice small dish for a drink, however, and as such, I like hijiki now. (Regarding arsenic contained in Hijiki, please refer to the footnote.)
Hijiki comes dried and usually has two different kinds; "Me-hijiki" 芽ひじき consisting of the buds or tips of hijiki, and "Naga-hijiki" 長ひじき consisting of the stalks of hijiki. I happened to get dried "Naga-hijiki" and decided to make two dishes. In dried form, hijiki is very hard and black like tangles of black metal wires. To prepare, after washing in cold running water in a colander, I soak it in large amount of cold water initially for 30 minutes. At the end of the 30 minutes, the volume of hijiki increases something like 10 fold and you can see the dark brown shapes of the original hijiki plant with the fresh smell of the ocean. I drain and wash in cold running water in a colander. I then soak again in fresh water. I repeat this several times over the period of about 2 hours (you do not really need this long soak and changes of water but I like to leach out as much of the small amount of arsenic as possible, see the footnote). If I am not ready to cook this immediately I keep it in a container with water and place it in the refrigerator.
1. Hijiki and chicken salad ひじきと鶏肉のサラダ
Since I had some leftover cooked (barbecued) whole chicken, I used the breast meat for this dish. If you are making this from scratch, you should either steam in sake or "sakamushi*" 酒蒸し or microwave the chicken breasts.
*add 2-3 tbs of sake in a small frying pan and add a chicken breast (skin removed). Put on a tight fitting lid and braise/steam for 4-5 minutes or until the chicken is done in a low flame.
2. Stewed Hijiki ひじきの煮物
This is as classic as hijiki dishes go. There are many variations to this. Some add cooked (yellow or ripe) soy beans "mizuni daizu" 水煮大豆 and other vegetables. Carrot and deep-fried tofu pouch "abura-age" 油揚げ are most common ingredients in this dish. I used carrot, sweet potato, edamame 枝豆 and deep fried tofu pouch in mine.
We had both hijiki dishes at one sitting. Both dishes are quite different in taste and texture (although it may look similar) and went well with cold sake.
*Footnote regrading arsenic in Hijiki:
I did not know this until I read Hiroyuki's blog some time ago. It appears that the amount of inorganic arsenic is not high enough to have a serous health concern if you consume hijiki in moderation (meaning not eat tons of hijiki everyday). There is no known case of arsenic health effects even in Japan where people tend to eat more seaweed than anywhere else including hijiki. It is also reported that If you soak hijiki for 1 hour and if you boil it for 5 minutes after hydration, . This time, I soaked much longer than needed with multiple changes of water which, I am surmising, reasonably reduced the arsenic content. So it appears that consuming hijiki cooked this way is not to be of any health concern. A (professional) well-informed Japanese food blogger appears to take a similar position.