Together, alone, as is, without asking
Set phrases that give the circumstances of an action (with others, by yourself, leaving things as they are, or without asking anyone), and all fit before a verb like iku.
issho ni
together (with)
一緒に いっしょに
Says an action is shared, with 'X to issho ni' meaning with X. It is the core of every invitation (issho ni ikou, issho ni iku?).
issho ni iku?
Want to come with me?
一緒に行く？
issho ni ikimasen ka?
Would you like to come along?
一緒に行きませんか？
issho without ni means 'the same': issho da ne = same here. Polite invitations use -masen ka (issho ni ikimasen ka); casual can be iku? or ikanai?
Learn alongside: hitori de
hitori de
alone; by oneself
一人で ひとりで
Says you do something on your own, either without company or without help (hitori de dekiru).
hitori de iku?
Are you going by yourself?
一人で行く？
hitori de ikimasu ka?
Are you going alone?
一人で行きますか？
Two people is futari de.
Learn alongside: issho ni
kono mama
as it is; like this
このまま
Keeps the current situation unchanged, as in 'kono mama de ii' (fine like this) and 'kono mama ja dame' (can't go on like this).
kono mama de ii yo.
It's fine like this.
このままでいいよ。
kono mama de ii desu yo.
It's fine like this.
このままでいいですよ。
kono mama ja... warns where things are heading if nothing changes.
sono mama
as is; just like that; straight on
そのまま
Leaves something as it is (sono mama de ii = leave it as is, no need to change anything), or carries straight on without a further step (sono mama kaetta = went straight home; sono mama mattete = just wait there).
sono mama kaetta.
I went straight home.
そのまま帰った。
sono mama kaerimashita.
I went straight home.
そのまま帰りました。
To a clerk offering a bag or wrapping, sono mama de ii desu means 'it's fine as it is'. Said to a person, sono mama de ii also reassures: you're fine as you are. sono mama omachi kudasai (please hold) is the fixed phone and shop line.
katte ni
without asking; as one pleases; by itself (automatically)
勝手に かってに
Goes before a verb to say something was done without asking or permission (katte ni kimeta, katte ni tabeta), or that it happened by itself with nobody doing it (doa ga katte ni shimatta). Mostly it's a complaint, but with -te ii it gives free rein (katte ni tabete ii yo = help yourself), and turned on yourself it's an apology (katte ni tsukatte gomen / sumimasen = sorry for using it without asking).
katte ni kimenaide yo.
Don't go deciding things without asking me!
勝手に決めないでよ。
katte ni kimenaide kudasai.
Please don't decide things without asking.
勝手に決めないでください。
katte ni shite! on its own is a huffy 'suit yourself'. By ear it matches katte from kau (buy), pitch included, so only the ni tells them apart: katte kita (went and bought it) vs katte ni kita (came without being asked). katte from katsu (win) has a different pitch.