As promised I have uploaded the "Welcome to the NHK" OSTs that I have been able to find. Pearl Kyoudai(Pearl Brothers) is one of my favorite j-artists and I thought I would share it all with the other NHK fans. I honestly can't get enough of Hitori Bocchi..
Artists include: Pearl Kyoudai, ROUND TABLE feat. Nino, Makino Yui, Kenji Ohtsuki & Fumihiko Kitsu.
All tracks included are listed below.
Download:
Welcome to the NHK OST
Enjoy.
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Dark Side ni Youkoso ( Welcome to the Dark Side ): [[Pearl Kyoudai]] 
Tracklist:
1. Ashita wa Tabun Overture
2. Ikasuze! Positive Thinking
3. Sekai wa Boku wo Naguri ni Kuru
4. Kimi ni Kuzure e ho e
5. Kyou wa Yuuhi Yarou
6. Natsu no Nichi ni Youkoso!
7. Jumbo Camera ni Donto Koi!
8. Ashita wa Tabun Daijoubu
9. Shuraba ni Youkoso!
10. Mushiburo to Nou to Tanin
11. Dark Side ni Tsuitekite
12. Youkoso! Hitori Bocchi
13. Inbou wa Yoake ni Warau
14. Yoru wa Fuwari Kaze wa Hirari
15. Daijoubu Call
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Sunny Side ni Youkoso ( Welcome to the Sunny Side ): [[Pearl Kyoudai]] 
Tracklist:
1. Ana no wa Makkuro ke
2. Nippon Bikikomori Kyoukai no Theme
3. Puzzle -extra hot mix-
4. Himitsu no Sen wo Hiku Yatsura
5. Omae to Ore no Enjou Douro
6. Kimi no Corona ni Tsutsumaretai
7. Gosui ni Tarasu Tsuri Ito
8. Fushigi Purupuru Pururin Rin!
9. Suishoutai Haran
10. Bokura ga Itsumo Kaeru Basho
11. Maken yo Sekai wo Kiri Hirakero
12. DIG Battle DIG
13. Kumori Nochi, Michinori
14. Happiness ni Youkoso!
15. Kyuukei wa Ama Sugiru Kotoba
16. Tenshi wa Namida to Tsubasa wo Otosu
17. Hitori no Tame no Lullaby
18. Kagerou Ressha
19. Koi wa Houkago no Youni
20. Owari wo Mitsumeru Shunkan
21. Moratoriamu ni Youkoso!
22. Odoru Akachan Ningen
23. Modokashii Sekai no Ue de -piano ver.-
24. Fushigi Purupuru Pururin Rin! -Denpa ver.-
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Puzzle ( NHK Opening Single ):
Tracks:
01. Puzzle
02. Atashi Datte Onaji Koto Omotteru yo
03. Puzzle (instrumental)
04. Atashi Datte Onaji Koto Omotteru yo (instrumental)
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ED 1 Single: Odoru Akachan Ningen 
Tracks:
01. Odoru Akachan Ningen
02. N H K Kyoukai Theme
03. Odoru Dame Ningen
04. Odoru Akachan Ningen -instrumental-
05. N H K Kyoukai Theme -instrumental-
06. Odoru Dame Ningen -instrumental-
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ED2 Single: Madokashii Sekai no Ue de 
Tracklist:1. Madokashii Sekai no Ue de
2. Dark Side Nitsuite Kite -New Mix-
3. Madokashii Sekai no Ue de (Instrumental)
4. Dark Side Nitsuite Kite -New Mix- (Instrumental)