I am looking for a series that includes the main character taking care of someone much younger, for example becoming a older brother for a fox girl slave he saved or a world traveler salaryman becoming a dad for a demon kid. The recommendations do not have to have this criteria as the focus, as long as it has it pretty often. The ones i am already reading include "Because I’m a Weapons Shop Uncle", "Uchi no Musume no Tame naraba Ore wa Moshikashitara Maou mo Taoseru kamo Shirenai"
http://www.novelupdates.com/series/samayou-shinki-no-duelist/ Maybe? Lemme see if I can find more. Also do you want slice of life only? Or do you want more than just that? Ah, though it's not all fluffy and is more action orientated but it has an older MC looking after a (supposedly) younger one.
10 nen goshi no Hiki-NEET o Yamete Gaishutsushitara Jitaku goto Isekai ni Ten’ishiteta EDIT: In regards to Samayou Shinki Duelist, I would suggest you'd think twice about picking it up. It is finished in two volumes, without proper ending.
Corseltel series. The Dragon mages borrow powers from the dragons and they protect them in return . the another duty is to take care of the dragon children. This is the story of the most powerful dragon nanny*ahem* mage .
10 nen & Uchi musume which I would've mentioned first have already been mentioned, so let's see... http://www.novelupdates.com/series/evil-god-average/ - The MC becomes a sort of Big Sister Master to two younger girls who otherwise would be on a worse situation. http://www.novelupdates.com/series/garudeina-oukoku-koukoku-ki/ - The MC takes a beastgirl slave as his younger sister http://www.novelupdates.com/series/marginal-operation/ - MC takes a platoon of children under his wing to 'raise' http://www.novelupdates.com/series/shuras-wrath/ - MC with a mysterious background becomes a big brother for a younger girl, and then her parents die and she gets a serious disease, so he's all she's got http://www.novelupdates.com/series/...mination-building-a-slave-harem-from-scratch/ - MC gets 3 younger Beastgirls as slave maids, one as normal and two in order to keep them safe from worse people http://www.novelupdates.com/series/tate-no-yuusha-no-nariagari/ - MC gets a young beastgirl slave, and properly raises her to become a proper adult / adventurer , overcoming a few of her traumas, and later takes care of other similar cases http://www.novelupdates.com/series/world-teacher-other-world-style-education-agent/ - MC becomes a teacher / father figure / big brother / master / romantic interest to a pair of beastpeople siblings