not all of the characters are smart, but they do use their knowledge to an extent, whether it may be their nature or their previous life knowledge. some may be considered op, but focus more on their knowledge rather than their powers.
http://www.mangago.zone/read-manga/i_m_a_villainous_daughter_so_i_m_going_to_keep_the_last_boss/ mc is naturally smart.
http://www.mangago.zone/read-manga/ascendance_of_a_bookworm/ the mc has magic, but it focuses more on her using her knowledge to make things from her previous like like sweets and hair accessories
http://www.mangago.zone/read-manga/the_banished_villainess_living_the_leisurely_life_of_a_nun_making_revolutionary_church_food/ mc uses her knowledge to make food from her previous life.
http://www.mangago.zone/read-manga/jishou_akuyaku_reijou_na_konyakusha_no_kansatsu_kiroku/ the ML is smart and manipulative in a way, but it focuses more on the romance and a bit of comedy.
http://www.mangago.zone/read-manga/tensei_saki_ga_sh_jo_manga_no_hakuton_reij_datta/ not that much progress yet in the manga, but when i read the novel, mc also creates stuff from previous life.
http://www.mangago.zone/read-manga/isekai_yakkyoku/ the mc is op, but it focuses more on using his knowledge as a doctor in his previous life.
http://www.mangago.zone/read-manga/the_justice_of_villainous_woman/ mc is also naturally smart.
http://www.mangago.zone/read-manga/drop_a_tale_of_the_fragrance_princess/ mc is smart and does experiments, but not focused on that, and the story ended abruptly.
http://www.mangago.zone/read-manga/chitra/ the mc is op in a way, because of her familiars. but she is also smart and uses her knowledge to run a town as a noble.
http://www.mangago.zone/read-manga/empress_of_another_world/?av=1 mc is smart in a way, but if i remember correctly, there was more focus on the plot and romance.
http://www.mangago.zone/read-manga/lady_rose_wants_to_be_a_commoner/ mc is also smart but not that much progress.
http://www.mangago.zone/read-manga/i_swear_i_won_t_bother_you_again/ mc is smart and talented but it focuses more on the plot i guess.
http://www.mangago.zone/read-manga/iris_lady_with_a_smartphone/ mc is smart and uses her previous life knowledge in making things.
http://www.mangago.zone/read-manga/of_course_i_ll_claim_palimony/ mc is a smart businesswoman.
http://www.mangago.zone/read-manga/isekai_de_caf_o_kaiten_shimashita/ mc also uses her knowledge to make food from her previous world.
http://www.mangago.zone/read-manga/rebirth_of_villianous_life_of_letizia_after_engagement_abandonment/ mc was originally smart and after remembering her past life, she uses her knowledge as a nurse before.
http://www.mangago.zone/read-manga/magic_artisan_dahliya_won_t_hang_her_head_a_free_craftsman_life_from_now_on/ mc is skilled in inventing.
http://www.mangago.zone/read-manga/the_alchemist_who_survived_now_dreams_of_a_quiet_city_life/ not much progress but mc is a skilled alchemist.
http://www.mangago.zone/read-manga/the_duchess_50_tea_recipes/ mc uses her knowledge in tea making and also in business but romance is a focus in the story.
http://www.mangago.zone/read-manga/the_princess_likes_to_lie/ no progress yet but seems like the mc is a smart princess.
http://www.mangago.zone/read-manga/a_capable_maid/ not necessarily smart, but mc uses knowledge from her 'dreams' and applies them in her life as a maid.
http://www.mangago.zone/read-manga/kakuriyo_no_yadomeshi_ayakashi_oyado_ni_yomeiri_shimasu/ mc uses her cooking skills in the youkai world.
http://www.mangago.zone/read-manga/herscherik_the_epic_of_the_reincarnated_prince/ mc is a kid who rises up to fight the corrupt nobles.
http://www.mangago.zone/read-manga/beatrice/ mc has knowledge in the medicine field.
http://www.mangago.zone/read-manga/i_choose_the_emperor_ending/ mc is smart and invents things.
http://www.mangago.zone/read-manga/the_villainess_reverses_the_hourglass/ mc becomes cunning and uses her own strategies to become a 'villainess'.
http://www.mangago.zone/read-manga/the_princess_spaceship/ mc was an astronaut transported to another world.
http://www.mangago.zone/read-manga/charlotte_has_five_disciples/ mc was originally smart and was also op, but her magic has been different ever since she 'died'. now focuses more on her op disciples revolving around her. i'm predicting that she'll uses her op powers somehow in the future.
http://www.mangago.zone/read-manga/what_kind_of_empress_is_this/ mc isn't exactly smart, but is good at talking, because she was a customer service agent.
http://www.mangago.zone/read-manga/the_stereotypical_life_of_a_reincarnated_lady/ mc is somehow nonchalant, but retaliates if needed, so she struck me as someone smart. http://www.mangago.zone/read-manga/medical_return/ incredibly smart and hardworking mc in the medical field.
can you guys recommend a manga with a non- OP MC? similar to "Sengoku Komachi Kurou Tan!" where the MC is just a knowledgeable person from the present time with no powers, just smarts?
I'm kind of tired of reading OP MC with little to no challenge in their problems, and is just basically a power flexer.