Any good Sci-fi with a loner/ruthless protag? No harem would be nice. If he is op even better! No Yaoi, or Female protag
I know some sort of scifi stories that fit. "Nano Machine (retranslated)" despite the name has only one scifi feature, being the obvious nano-machines, but the rest of the setting is wuxia. And the mc stops being a loner after a while. "Superstars of Tomorrow" is scifi but its mostly slice of life, and while the mc is somewhat a loner and ruthless when fighting, he is a "normal" person the most of the time. "The Card Apprentice" is scifish fantasy, and the mc is somewhat coldhearted, but this guy too forms a group at some point. "Legend of the supreme soldier" has a pretty ruthless (wild) protagonist, and even when he eventually forms a group (late in the story) he still has a bit of a loner mentality. "Forty milleniums of cultivation" the protag isnt exactly ruthless, and the setting is xianxiaish scifi, but he acts alone most of the time "Shadow hack" the protag has the ability to make shadow clone and so doesnt even need a group "Monster Paradise" the mc is mostly loner. sorry that im a bit weak on the 'ruthless' part but i dont like actually evil protags
lol the MC has a lot of player and friend NPC , thats not loner and the MC is not ruthless , just rational