Any good, beautiful oneshots (amazing art and plot) that's under 20 pages? Any kind of gen...

I don't know about less than 20 pages, but these are some of my favorite oneshots. (which are a lot cause I absolutely adore good oneshots)

http://www.mangago.zone/read-manga/mou_tamago_wa_korosanai/
http://www.mangago.zone/read-manga/tonari_no_kanata/
http://www.mangago.zone/read-manga/yume_kurai/
http://www.mangago.zone/read-manga/hana_to_shokutaku/
http://www.mangago.zone/read-manga/ryuu_to_hidari_te/
http://www.mangago.zone/read-manga/yonjuukyuu/
http://www.mangago.zone/read-manga/then_i_ll_go_first/
http://www.mangago.zone/read-manga/makka_na_tulip_o_kimi_ni/
http://www.mangago.zone/read-manga/kuroorihime_to_kawaki_no_ou/
http://www.mangago.zone/read-manga/sayonara_kodomotachi/
http://www.mangago.zone/read-manga/kao_no_nai_otoko/
http://www.mangago.zone/read-manga/soko_wa_chuumon_no_ooi_ryouriten/
http://www.mangago.zone/read-manga/akai_michi/
http://www.mangago.zone/read-manga/i_am_currently_living_with_a_bear/
http://www.mangago.zone/read-manga/shisei_yokobaba_ryo/
http://www.mangago.zone/read-manga/yorimichi_re/
http://www.mangago.zone/read-manga/daisuki_datta_yo_sensei/
http://www.mangago.zone/read-manga/kanojo_no_namida_ga_yuki_da_toshitara/
http://www.mangago.zone/read-manga/nemurenu_ou_ni_sasagu_yogatari/ (a series of interconnected oneshots. Specially love the second chapter)

20 pages OR under:
http://www.mangago.zone/read-manga/trap_min_song_a/
http://www.mangago.zone/read-manga/hakoiri_musuko/
http://www.mangago.zone/read-manga/indirect_kiss/
http://www.mangago.zone/read-manga/deep_bloody_night/
http://www.mangago.zone/read-manga/honto_no_uso/
http://www.mangago.zone/read-manga/tsujimura_san_is_a_secret/
http://www.mangago.zone/read-manga/wake_me_up/
http://www.mangago.zone/read-manga/something_happening/
http://www.mangago.zone/read-manga/senaka_kara_daite/ (ch.3,5,6,8,9)
http://www.mangago.zone/read-manga/the_king_and_the_attendant/
http://www.mangago.zone/read-manga/boys_love_nakamura_asumiko/
http://www.mangago.zone/read-manga/urban_cross/
http://www.mangago.zone/read-manga/ookami_gui/
http://www.mangago.zone/read-manga/one_night_resort/
http://www.mangago.zone/read-manga/isshunsaki_wa_koi/
http://www.mangago.zone/read-manga/hana_aogu/
http://www.mangago.zone/read-manga/call_my_name_jaryuu_dokuro/
http://www.mangago.zone/read-manga/mousou_otoko/
http://www.mangago.zone/read-manga/so_serious/
http://www.mangago.zone/read-manga/laundry/
http://www.mangago.zone/read-manga/akai_hana/
http://www.mangago.zone/read-manga/baked_sweet_glasses/

22 pages. As close as I could get (⌒▽⌒) http://www.mangago.zone/read-manga/kaze_ni_chiru_hanabira_to_kisu/

http://www.mangago.zone/home/mangalist/14402/